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 $53.39   9.623%   $58.5277   $58.53   $58.55   $58.50  
  Purchase #2 $191.40   12.829%   $215.9547   $215.95   $215.95   $216.00  
  Purchase #3 $49.68   5.463%   $52.394   $52.39   $52.40   $52.40  
  Purchase #4 $88.54   11.502%   $98.7239   $98.72   $98.70   $98.70  
  Purchase #5 $180.68   5.761%   $191.089   $191.09   $191.10   $191.10  
  Purchase #6 $62.78   7.437%   $67.4489   $67.45   $67.45   $67.40  
  Purchase #7 $81.68   3.712%   $84.712   $84.71   $84.70   $84.70  
  7 purchase totals = $708.15       $768.8502   $768.84   $768.85   $768.80