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 $238.79   11.508%   $266.27   $266.27   $266.25   $266.30  
  Purchase #2 $187.68   3.191%   $193.6689   $193.67   $193.65   $193.70  
  Purchase #3 $60.53   6.312%   $64.3507   $64.35   $64.35   $64.40  
  Purchase #4 $75.81   10.315%   $83.6298   $83.63   $83.65   $83.60  
  Purchase #5 $214.30   3.565%   $221.9398   $221.94   $221.95   $221.90  
  Purchase #6 $166.87   3.254%   $172.2999   $172.30   $172.30   $172.30  
  Purchase #7 $101.71   10.566%   $112.4567   $112.46   $112.45   $112.50  
  7 purchase totals = $1,045.69       $1,114.6158   $1,114.62   $1,114.60   $1,114.70