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 $113.83   8.243%   $123.213   $123.21   $123.20   $123.20  
  Purchase #2 $53.79   6.646%   $57.3649   $57.36   $57.35   $57.40  
  Purchase #3 $132.72   3.207%   $136.9763   $136.98   $137.00   $137.00  
  Purchase #4 $81.68   4.733%   $85.5459   $85.55   $85.55   $85.50  
  Purchase #5 $216.67   12.216%   $243.1384   $243.14   $243.15   $243.10  
  Purchase #6 $232.68   12.272%   $261.2345   $261.23   $261.25   $261.20  
  Purchase #7 $51.39   13.446%   $58.2999   $58.30   $58.30   $58.30  
  7 purchase totals = $882.76       $965.7729   $965.77   $965.80   $965.70