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 $234.68   5.663%   $247.9699   $247.97   $247.95   $248.00  
  Purchase #2 $16.96   9.617%   $18.591   $18.59   $18.60   $18.60  
  Purchase #3 $199.78   5.187%   $210.1426   $210.14   $210.15   $210.10  
  Purchase #4 $216.51   10.812%   $239.9191   $239.92   $239.90   $239.90  
  Purchase #5 $10.52   5.769%   $11.1269   $11.13   $11.15   $11.10  
  Purchase #6 $73.88   6.402%   $78.6098   $78.61   $78.60   $78.60  
  Purchase #7 $197.74   9.362%   $216.2524   $216.25   $216.25   $216.30  
  7 purchase totals = $950.07       $1,022.6117   $1,022.61   $1,022.60   $1,022.60