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 $44.67   8.158%   $48.3142   $48.31   $48.30   $48.30  
  Purchase #2 $211.52   11.294%   $235.4091   $235.41   $235.40   $235.40  
  Purchase #3 $100.41   8.269%   $108.7129   $108.71   $108.70   $108.70  
  Purchase #4 $126.69   4.430%   $132.3024   $132.30   $132.30   $132.30  
  Purchase #5 $206.39   13.684%   $234.6324   $234.63   $234.65   $234.60  
  Purchase #6 $118.87   5.644%   $125.579   $125.58   $125.60   $125.60  
  Purchase #7 $101.82   6.515%   $108.4536   $108.45   $108.45   $108.50  
  7 purchase totals = $910.37       $993.4036   $993.39   $993.40   $993.40