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 $55.62   8.816%   $60.5235   $60.52   $60.50   $60.50  
  Purchase #2 $97.38   13.177%   $110.2118   $110.21   $110.20   $110.20  
  Purchase #3 $196.57   11.796%   $219.7574   $219.76   $219.75   $219.80  
  Purchase #4 $34.67   11.111%   $38.5222   $38.52   $38.50   $38.50  
  Purchase #5 $227.64   7.756%   $245.2958   $245.30   $245.30   $245.30  
  Purchase #6 $190.71   12.157%   $213.8946   $213.89   $213.90   $213.90  
  Purchase #7 $104.94   13.426%   $119.0292   $119.03   $119.05   $119.00  
  7 purchase totals = $907.53       $1,007.2345   $1,007.23   $1,007.20   $1,007.20