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 $234.92   3.196%   $242.428   $242.43   $242.45   $242.40  
  Purchase #2 $125.25   8.813%   $136.2883   $136.29   $136.30   $136.30  
  Purchase #3 $69.95   3.858%   $72.6487   $72.65   $72.65   $72.60  
  Purchase #4 $43.74   7.316%   $46.94   $46.94   $46.95   $46.90  
  Purchase #5 $165.88   7.639%   $178.5516   $178.55   $178.55   $178.60  
  Purchase #6 $183.52   10.371%   $202.5529   $202.55   $202.55   $202.60  
  Purchase #7 $44.85   5.199%   $47.1818   $47.18   $47.20   $47.20  
  7 purchase totals = $868.11       $926.5913   $926.59   $926.65   $926.60