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 $58.30   3.737%   $60.4787   $60.48   $60.50   $60.50  
  Purchase #2 $219.53   9.506%   $240.3985   $240.40   $240.40   $240.40  
  Purchase #3 $61.61   5.588%   $65.0528   $65.05   $65.05   $65.10  
  Purchase #4 $34.33   11.507%   $38.2804   $38.28   $38.30   $38.30  
  Purchase #5 $13.54   9.708%   $14.8545   $14.85   $14.85   $14.90  
  Purchase #6 $188.78   11.425%   $210.3481   $210.35   $210.35   $210.30  
  Purchase #7 $74.91   3.184%   $77.2951   $77.30   $77.30   $77.30  
  7 purchase totals = $651.00       $706.7081   $706.71   $706.75   $706.80