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 $54.92   7.382%   $58.9742   $58.97   $58.95   $59.00  
  Purchase #2 $23.88   4.533%   $24.9625   $24.96   $24.95   $25.00  
  Purchase #3 $78.26   6.534%   $83.3735   $83.37   $83.35   $83.40  
  Purchase #4 $190.66   4.860%   $199.9261   $199.93   $199.95   $199.90  
  Purchase #5 $206.64   10.398%   $228.1264   $228.13   $228.15   $228.10  
  Purchase #6 $206.71   8.579%   $224.4437   $224.44   $224.45   $224.40  
  Purchase #7 $118.56   8.142%   $128.2132   $128.21   $128.20   $128.20  
  7 purchase totals = $879.63       $948.0196   $948.01   $948.00   $948.00