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 $243.62   9.585%   $266.971   $266.97   $266.95   $267.00  
  Purchase #2 $74.25   4.335%   $77.4687   $77.47   $77.45   $77.50  
  Purchase #3 $115.41   13.672%   $131.1889   $131.19   $131.20   $131.20  
  Purchase #4 $225.61   13.811%   $256.769   $256.77   $256.75   $256.80  
  Purchase #5 $204.99   9.588%   $224.6444   $224.64   $224.65   $224.60  
  Purchase #6 $172.45   13.624%   $195.9446   $195.94   $195.95   $195.90  
  Purchase #7 $239.95   13.865%   $273.2191   $273.22   $273.20   $273.20  
  7 purchase totals = $1,276.28       $1,426.2057   $1,426.20   $1,426.15   $1,426.20