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 $50.81   4.664%   $53.1798   $53.18   $53.20   $53.20  
  Purchase #2 $200.87   9.173%   $219.2958   $219.30   $219.30   $219.30  
  Purchase #3 $33.95   4.321%   $35.417   $35.42   $35.40   $35.40  
  Purchase #4 $58.32   13.473%   $66.1775   $66.18   $66.20   $66.20  
  Purchase #5 $245.40   7.576%   $263.9915   $263.99   $264.00   $264.00  
  Purchase #6 $71.35   8.429%   $77.3641   $77.36   $77.35   $77.40  
  Purchase #7 $223.98   5.644%   $236.6214   $236.62   $236.60   $236.60  
  7 purchase totals = $884.68       $952.0471   $952.05   $952.05   $952.10