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 $41.31   6.601%   $44.0369   $44.04   $44.05   $44.00  
  Purchase #2 $196.85   9.783%   $216.1078   $216.11   $216.10   $216.10  
  Purchase #3 $231.94   5.478%   $244.6457   $244.65   $244.65   $244.60  
  Purchase #4 $113.28   9.466%   $124.0031   $124.00   $124.00   $124.00  
  Purchase #5 $90.86   4.529%   $94.975   $94.98   $95.00   $95.00  
  Purchase #6 $103.78   3.618%   $107.5348   $107.53   $107.55   $107.50  
  Purchase #7 $148.67   8.462%   $161.2505   $161.25   $161.25   $161.30  
  7 purchase totals = $926.69       $992.5538   $992.56   $992.60   $992.50