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 $204.43   13.854%   $232.7517   $232.75   $232.75   $232.80  
  Purchase #2 $209.36   11.252%   $232.9172   $232.92   $232.90   $232.90  
  Purchase #3 $184.50   9.594%   $202.2009   $202.20   $202.20   $202.20  
  Purchase #4 $164.67   7.717%   $177.3776   $177.38   $177.40   $177.40  
  Purchase #5 $88.74   5.864%   $93.9437   $93.94   $93.95   $93.90  
  Purchase #6 $23.87   10.547%   $26.3876   $26.39   $26.40   $26.40  
  Purchase #7 $69.50   10.429%   $76.7482   $76.75   $76.75   $76.70  
  7 purchase totals = $945.07       $1,042.3269   $1,042.33   $1,042.35   $1,042.30