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 $60.97   3.798%   $63.2856   $63.29   $63.30   $63.30  
  Purchase #2 $200.86   4.716%   $210.3326   $210.33   $210.35   $210.30  
  Purchase #3 $51.50   6.663%   $54.9314   $54.93   $54.95   $54.90  
  Purchase #4 $48.75   4.849%   $51.1139   $51.11   $51.10   $51.10  
  Purchase #5 $59.43   3.143%   $61.2979   $61.30   $61.30   $61.30  
  Purchase #6 $117.94   12.735%   $132.9597   $132.96   $132.95   $133.00  
  Purchase #7 $243.36   10.710%   $269.4239   $269.42   $269.40   $269.40  
  7 purchase totals = $782.81       $843.3450   $843.34   $843.35   $843.30