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 $93.71   11.797%   $104.765   $104.77   $104.75   $104.80  
  Purchase #2 $139.84   12.284%   $157.0179   $157.02   $157.00   $157.00  
  Purchase #3 $24.77   9.117%   $27.0283   $27.03   $27.05   $27.00  
  Purchase #4 $12.70   3.188%   $13.1049   $13.10   $13.10   $13.10  
  Purchase #5 $224.99   8.223%   $243.4909   $243.49   $243.50   $243.50  
  Purchase #6 $172.84   4.605%   $180.7993   $180.80   $180.80   $180.80  
  Purchase #7 $115.48   7.360%   $123.9793   $123.98   $124.00   $124.00  
  7 purchase totals = $784.33       $850.1856   $850.19   $850.20   $850.20