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 $40.51   8.638%   $44.0093   $44.01   $44.00   $44.00  
  Purchase #2 $175.95   4.322%   $183.5546   $183.55   $183.55   $183.60  
  Purchase #3 $104.91   6.427%   $111.6526   $111.65   $111.65   $111.70  
  Purchase #4 $243.35   11.386%   $271.0578   $271.06   $271.05   $271.10  
  Purchase #5 $64.94   11.411%   $72.3503   $72.35   $72.35   $72.40  
  Purchase #6 $20.97   9.716%   $23.0074   $23.01   $23.00   $23.00  
  Purchase #7 $117.39   6.725%   $125.2845   $125.28   $125.30   $125.30  
  7 purchase totals = $768.02       $830.9165   $830.91   $830.90   $831.10