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 $29.74   13.733%   $33.8242   $33.82   $33.80   $33.80  
  Purchase #2 $201.93   12.210%   $226.5857   $226.59   $226.60   $226.60  
  Purchase #3 $25.48   9.378%   $27.8695   $27.87   $27.85   $27.90  
  Purchase #4 $210.42   13.475%   $238.7741   $238.77   $238.75   $238.80  
  Purchase #5 $9.82   4.267%   $10.239   $10.24   $10.25   $10.20  
  Purchase #6 $165.39   10.570%   $182.8717   $182.87   $182.85   $182.90  
  Purchase #7 $230.75   10.855%   $255.7979   $255.80   $255.80   $255.80  
  7 purchase totals = $873.53       $975.9621   $975.96   $975.90   $976.00