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 $119.71   4.722%   $125.3627   $125.36   $125.35   $125.40  
  Purchase #2 $203.97   10.218%   $224.8117   $224.81   $224.80   $224.80  
  Purchase #3 $249.33   9.126%   $272.0839   $272.08   $272.10   $272.10  
  Purchase #4 $106.97   8.230%   $115.7736   $115.77   $115.75   $115.80  
  Purchase #5 $17.46   10.777%   $19.3417   $19.34   $19.35   $19.30  
  Purchase #6 $81.27   13.800%   $92.4853   $92.49   $92.50   $92.50  
  Purchase #7 $10.41   3.172%   $10.7402   $10.74   $10.75   $10.70  
  7 purchase totals = $789.12       $860.5991   $860.59   $860.60   $860.60