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 $86.32   13.243%   $97.7514   $97.75   $97.75   $97.80  
  Purchase #2 $144.46   7.384%   $155.1269   $155.13   $155.15   $155.10  
  Purchase #3 $241.70   12.327%   $271.4944   $271.49   $271.50   $271.50  
  Purchase #4 $242.62   13.467%   $275.2936   $275.29   $275.30   $275.30  
  Purchase #5 $158.31   13.302%   $179.3684   $179.37   $179.35   $179.40  
  Purchase #6 $234.93   6.507%   $250.2169   $250.22   $250.20   $250.20  
  Purchase #7 $33.38   7.670%   $35.9402   $35.94   $35.95   $35.90  
  7 purchase totals = $1,141.72       $1,265.1918   $1,265.19   $1,265.20   $1,265.20