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 $42.31   6.577%   $45.0927   $45.09   $45.10   $45.10  
  Purchase #2 $18.82   8.220%   $20.367   $20.37   $20.35   $20.40  
  Purchase #3 $125.87   7.127%   $134.8408   $134.84   $134.85   $134.80  
  Purchase #4 $81.96   11.343%   $91.2567   $91.26   $91.25   $91.30  
  Purchase #5 $164.53   9.788%   $180.6342   $180.63   $180.65   $180.60  
  Purchase #6 $216.76   10.233%   $238.9411   $238.94   $238.95   $238.90  
  Purchase #7 $100.95   6.757%   $107.7712   $107.77   $107.75   $107.80  
  7 purchase totals = $751.20       $818.9037   $818.90   $818.90   $818.90