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 $156.92   6.540%   $167.1826   $167.18   $167.20   $167.20  
  Purchase #2 $213.57   3.532%   $221.1133   $221.11   $221.10   $221.10  
  Purchase #3 $64.41   8.261%   $69.7309   $69.73   $69.75   $69.70  
  Purchase #4 $94.76   12.477%   $106.5832   $106.58   $106.60   $106.60  
  Purchase #5 $60.48   5.137%   $63.5869   $63.59   $63.60   $63.60  
  Purchase #6 $133.92   9.532%   $146.6853   $146.69   $146.70   $146.70  
  Purchase #7 $66.69   11.486%   $74.35   $74.35   $74.35   $74.40  
  7 purchase totals = $790.75       $849.2322   $849.23   $849.30   $849.30