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 $84.86   12.567%   $95.5244   $95.52   $95.50   $95.50  
  Purchase #2 $103.62   12.192%   $116.2534   $116.25   $116.25   $116.30  
  Purchase #3 $212.44   10.609%   $234.9778   $234.98   $235.00   $235.00  
  Purchase #4 $137.37   10.247%   $151.4463   $151.45   $151.45   $151.40  
  Purchase #5 $14.72   8.367%   $15.9516   $15.95   $15.95   $16.00  
  Purchase #6 $96.83   10.449%   $106.9478   $106.95   $106.95   $106.90  
  Purchase #7 $39.78   6.424%   $42.3355   $42.34   $42.35   $42.30  
  7 purchase totals = $689.62       $763.4368   $763.44   $763.45   $763.40