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 $58.59   4.641%   $61.3092   $61.31   $61.30   $61.30  
  Purchase #2 $116.91   10.302%   $128.9541   $128.95   $128.95   $129.00  
  Purchase #3 $43.44   5.612%   $45.8779   $45.88   $45.90   $45.90  
  Purchase #4 $60.36   11.796%   $67.4801   $67.48   $67.50   $67.50  
  Purchase #5 $14.28   11.818%   $15.9676   $15.97   $15.95   $16.00  
  Purchase #6 $61.53   3.535%   $63.7051   $63.71   $63.70   $63.70  
  Purchase #7 $211.53   6.105%   $224.4439   $224.44   $224.45   $224.40  
  7 purchase totals = $566.64       $607.7379   $607.74   $607.75   $607.80