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 $88.79   8.679%   $96.4961   $96.50   $96.50   $96.50  
  Purchase #2 $237.43   10.394%   $262.1085   $262.11   $262.10   $262.10  
  Purchase #3 $18.36   7.486%   $19.7344   $19.73   $19.75   $19.70  
  Purchase #4 $62.75   4.109%   $65.3284   $65.33   $65.35   $65.30  
  Purchase #5 $203.97   10.428%   $225.24   $225.24   $225.25   $225.20  
  Purchase #6 $66.34   13.330%   $75.1831   $75.18   $75.20   $75.20  
  Purchase #7 $108.44   6.408%   $115.3888   $115.39   $115.40   $115.40  
  7 purchase totals = $786.08       $859.4793   $859.48   $859.55   $859.40