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 $207.58   9.391%   $227.0738   $227.07   $227.05   $227.10  
  Purchase #2 $10.78   6.507%   $11.4815   $11.48   $11.50   $11.50  
  Purchase #3 $226.82   8.391%   $245.8525   $245.85   $245.85   $245.90  
  Purchase #4 $203.84   6.855%   $217.8132   $217.81   $217.80   $217.80  
  Purchase #5 $48.47   13.818%   $55.1676   $55.17   $55.15   $55.20  
  Purchase #6 $157.30   6.171%   $167.007   $167.01   $167.00   $167.00  
  Purchase #7 $29.55   4.343%   $30.8334   $30.83   $30.85   $30.80  
  7 purchase totals = $884.34       $955.2290   $955.22   $955.20   $955.30