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 $58.59   11.821%   $65.5159   $65.52   $65.50   $65.50  
  Purchase #2 $99.64   11.346%   $110.9452   $110.95   $110.95   $110.90  
  Purchase #3 $34.32   7.387%   $36.8552   $36.86   $36.85   $36.90  
  Purchase #4 $121.29   3.273%   $125.2598   $125.26   $125.25   $125.30  
  Purchase #5 $137.86   6.319%   $146.5714   $146.57   $146.55   $146.60  
  Purchase #6 $76.31   7.427%   $81.9775   $81.98   $82.00   $82.00  
  Purchase #7 $215.98   9.428%   $236.3426   $236.34   $236.35   $236.30  
  7 purchase totals = $743.99       $803.4676   $803.48   $803.45   $803.50