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 $65.82   8.167%   $71.1955   $71.20   $71.20   $71.20  
  Purchase #2 $179.26   10.341%   $197.7973   $197.80   $197.80   $197.80  
  Purchase #3 $59.87   11.578%   $66.8017   $66.80   $66.80   $66.80  
  Purchase #4 $248.64   13.428%   $282.0274   $282.03   $282.05   $282.00  
  Purchase #5 $90.63   11.412%   $100.9727   $100.97   $100.95   $101.00  
  Purchase #6 $224.97   4.468%   $235.0217   $235.02   $235.00   $235.00  
  Purchase #7 $179.91   4.716%   $188.3946   $188.39   $188.40   $188.40  
  7 purchase totals = $1,049.10       $1,142.2109   $1,142.21   $1,142.20   $1,142.20