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 $179.39   8.687%   $194.9736   $194.97   $194.95   $195.00  
  Purchase #2 $32.54   9.798%   $35.7283   $35.73   $35.75   $35.70  
  Purchase #3 $152.30   5.576%   $160.7922   $160.79   $160.80   $160.80  
  Purchase #4 $20.53   8.117%   $22.1964   $22.20   $22.20   $22.20  
  Purchase #5 $98.32   3.216%   $101.482   $101.48   $101.50   $101.50  
  Purchase #6 $38.85   9.732%   $42.6309   $42.63   $42.65   $42.60  
  Purchase #7 $177.71   7.585%   $191.1893   $191.19   $191.20   $191.20  
  7 purchase totals = $699.64       $748.9927   $748.99   $749.05   $749.00