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 $187.62   11.831%   $209.8173   $209.82   $209.80   $209.80  
  Purchase #2 $62.86   3.573%   $65.106   $65.11   $65.10   $65.10  
  Purchase #3 $16.88   6.277%   $17.9396   $17.94   $17.95   $17.90  
  Purchase #4 $78.74   5.304%   $82.9164   $82.92   $82.90   $82.90  
  Purchase #5 $228.92   10.695%   $253.403   $253.40   $253.40   $253.40  
  Purchase #6 $130.77   13.593%   $148.5456   $148.55   $148.55   $148.50  
  Purchase #7 $133.91   12.796%   $151.0451   $151.05   $151.05   $151.00  
  7 purchase totals = $839.70       $928.7730   $928.79   $928.75   $928.60