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 $197.97   7.603%   $213.0217   $213.02   $213.00   $213.00  
  Purchase #2 $81.85   13.430%   $92.8425   $92.84   $92.85   $92.80  
  Purchase #3 $55.45   7.520%   $59.6198   $59.62   $59.60   $59.60  
  Purchase #4 $163.76   11.613%   $182.7774   $182.78   $182.80   $182.80  
  Purchase #5 $83.91   10.214%   $92.4806   $92.48   $92.50   $92.50  
  Purchase #6 $164.65   8.530%   $178.6946   $178.69   $178.70   $178.70  
  Purchase #7 $36.25   13.683%   $41.2101   $41.21   $41.20   $41.20  
  7 purchase totals = $783.84       $860.6467   $860.64   $860.65   $860.60