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 $224.75   13.629%   $255.3812   $255.38   $255.40   $255.40  
  Purchase #2 $196.62   9.413%   $215.1278   $215.13   $215.15   $215.10  
  Purchase #3 $69.78   5.686%   $73.7477   $73.75   $73.75   $73.70  
  Purchase #4 $18.77   9.526%   $20.558   $20.56   $20.55   $20.60  
  Purchase #5 $102.90   12.685%   $115.9529   $115.95   $115.95   $116.00  
  Purchase #6 $153.85   8.555%   $167.0119   $167.01   $167.00   $167.00  
  Purchase #7 $214.25   10.249%   $236.2085   $236.21   $236.20   $236.20  
  7 purchase totals = $980.92       $1,083.9880   $1,083.99   $1,084.00   $1,084.00