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 $191.89   11.676%   $214.2951   $214.30   $214.30   $214.30  
  Purchase #2 $84.77   12.814%   $95.6324   $95.63   $95.65   $95.60  
  Purchase #3 $23.58   9.235%   $25.7576   $25.76   $25.75   $25.80  
  Purchase #4 $53.45   4.597%   $55.9071   $55.91   $55.90   $55.90  
  Purchase #5 $221.58   4.213%   $230.9152   $230.92   $230.90   $230.90  
  Purchase #6 $247.91   6.435%   $263.863   $263.86   $263.85   $263.90  
  Purchase #7 $172.46   3.638%   $178.7341   $178.73   $178.75   $178.70  
  7 purchase totals = $995.64       $1,065.1045   $1,065.11   $1,065.10   $1,065.10