Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.61   3.188%   $203.9098   $203.91   $203.90   $203.90  
  Purchase #2 $229.49   10.236%   $252.9806   $252.98   $253.00   $253.00  
  Purchase #3 $149.30   9.109%   $162.8997   $162.90   $162.90   $162.90  
  Purchase #4 $215.61   10.437%   $238.1132   $238.11   $238.10   $238.10  
  Purchase #5 $153.28   5.286%   $161.3824   $161.38   $161.40   $161.40  
  Purchase #6 $116.98   13.112%   $132.3184   $132.32   $132.30   $132.30  
  Purchase #7 $205.46   4.255%   $214.2023   $214.20   $214.20   $214.20  
  7 purchase totals = $1,267.73       $1,365.8064   $1,365.80   $1,365.80   $1,365.80