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 $103.91   13.526%   $117.9649   $117.96   $117.95   $118.00  
  Purchase #2 $199.71   8.468%   $216.6214   $216.62   $216.60   $216.60  
  Purchase #3 $49.75   6.402%   $52.935   $52.94   $52.95   $52.90  
  Purchase #4 $32.67   4.813%   $34.2424   $34.24   $34.25   $34.20  
  Purchase #5 $76.71   6.225%   $81.4852   $81.49   $81.50   $81.50  
  Purchase #6 $208.58   11.201%   $231.943   $231.94   $231.95   $231.90  
  Purchase #7 $187.71   12.314%   $210.8246   $210.82   $210.80   $210.80  
  7 purchase totals = $859.04       $946.0165   $946.01   $946.00   $945.90