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 $22.98   8.578%   $24.9512   $24.95   $24.95   $25.00  
  Purchase #2 $179.87   8.391%   $194.9629   $194.96   $194.95   $195.00  
  Purchase #3 $150.98   4.380%   $157.5929   $157.59   $157.60   $157.60  
  Purchase #4 $22.79   13.469%   $25.8596   $25.86   $25.85   $25.90  
  Purchase #5 $210.61   8.746%   $229.03   $229.03   $229.05   $229.00  
  Purchase #6 $113.39   11.664%   $126.6158   $126.62   $126.60   $126.60  
  Purchase #7 $30.66   8.830%   $33.3673   $33.37   $33.35   $33.40  
  7 purchase totals = $731.28       $792.3797   $792.38   $792.35   $792.50