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 $45.38   10.204%   $50.0106   $50.01   $50.00   $50.00  
  Purchase #2 $199.70   7.619%   $214.9151   $214.92   $214.90   $214.90  
  Purchase #3 $26.59   12.553%   $29.9278   $29.93   $29.95   $29.90  
  Purchase #4 $64.38   12.270%   $72.2794   $72.28   $72.30   $72.30  
  Purchase #5 $189.34   6.257%   $201.187   $201.19   $201.20   $201.20  
  Purchase #6 $213.82   5.725%   $226.0612   $226.06   $226.05   $226.10  
  Purchase #7 $29.81   6.485%   $31.7432   $31.74   $31.75   $31.70  
  7 purchase totals = $769.02       $826.1243   $826.13   $826.15   $826.10