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 $60.49   3.730%   $62.7463   $62.75   $62.75   $62.70  
  Purchase #2 $174.32   11.269%   $193.9641   $193.96   $193.95   $194.00  
  Purchase #3 $133.47   9.206%   $145.7572   $145.76   $145.75   $145.80  
  Purchase #4 $58.95   5.266%   $62.0543   $62.05   $62.05   $62.10  
  Purchase #5 $23.64   13.512%   $26.8342   $26.83   $26.85   $26.80  
  Purchase #6 $37.62   7.323%   $40.3749   $40.37   $40.35   $40.40  
  Purchase #7 $104.97   7.812%   $113.1703   $113.17   $113.15   $113.20  
  7 purchase totals = $593.46       $644.9013   $644.89   $644.85   $645.00