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 $115.95   8.865%   $126.229   $126.23   $126.25   $126.20  
  Purchase #2 $53.69   8.613%   $58.3143   $58.31   $58.30   $58.30  
  Purchase #3 $53.30   10.171%   $58.7211   $58.72   $58.70   $58.70  
  Purchase #4 $197.78   9.363%   $216.2981   $216.30   $216.30   $216.30  
  Purchase #5 $60.47   9.700%   $66.3356   $66.34   $66.35   $66.30  
  Purchase #6 $115.84   8.107%   $125.2311   $125.23   $125.25   $125.20  
  Purchase #7 $29.97   4.844%   $31.4217   $31.42   $31.40   $31.40  
  7 purchase totals = $627.00       $682.5509   $682.55   $682.55   $682.40