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 $185.44   12.507%   $208.633   $208.63   $208.65   $208.60  
  Purchase #2 $62.53   11.186%   $69.5246   $69.52   $69.50   $69.50  
  Purchase #3 $41.34   11.733%   $46.1904   $46.19   $46.20   $46.20  
  Purchase #4 $210.53   5.251%   $221.5849   $221.58   $221.60   $221.60  
  Purchase #5 $111.91   7.578%   $120.3905   $120.39   $120.40   $120.40  
  Purchase #6 $228.87   7.274%   $245.518   $245.52   $245.50   $245.50  
  Purchase #7 $243.32   12.401%   $273.4941   $273.49   $273.50   $273.50  
  7 purchase totals = $1,083.94       $1,185.3355   $1,185.32   $1,185.35   $1,185.30