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 $101.76   9.400%   $111.3254   $111.33   $111.35   $111.30  
  Purchase #2 $64.26   12.655%   $72.3921   $72.39   $72.40   $72.40  
  Purchase #3 $146.48   11.418%   $163.2051   $163.21   $163.20   $163.20  
  Purchase #4 $26.72   4.726%   $27.9828   $27.98   $28.00   $28.00  
  Purchase #5 $126.86   8.427%   $137.5505   $137.55   $137.55   $137.60  
  Purchase #6 $144.60   13.521%   $164.1514   $164.15   $164.15   $164.20  
  Purchase #7 $240.95   4.308%   $251.3301   $251.33   $251.35   $251.30  
  7 purchase totals = $851.63       $927.9374   $927.94   $928.00   $928.00