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 $191.60   3.844%   $198.9651   $198.97   $198.95   $199.00  
  Purchase #2 $158.99   11.801%   $177.7524   $177.75   $177.75   $177.80  
  Purchase #3 $127.44   5.339%   $134.244   $134.24   $134.25   $134.20  
  Purchase #4 $245.97   12.247%   $276.0939   $276.09   $276.10   $276.10  
  Purchase #5 $70.62   7.118%   $75.6467   $75.65   $75.65   $75.60  
  Purchase #6 $25.61   8.354%   $27.7495   $27.75   $27.75   $27.70  
  Purchase #7 $146.47   12.148%   $164.2632   $164.26   $164.25   $164.30  
  7 purchase totals = $966.70       $1,054.7148   $1,054.71   $1,054.70   $1,054.70