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 $62.75   3.792%   $65.1295   $65.13   $65.15   $65.10  
  Purchase #2 $206.71   9.722%   $226.8063   $226.81   $226.80   $226.80  
  Purchase #3 $214.37   8.527%   $232.6493   $232.65   $232.65   $232.60  
  Purchase #4 $28.91   5.537%   $30.5107   $30.51   $30.50   $30.50  
  Purchase #5 $114.92   5.460%   $121.1946   $121.19   $121.20   $121.20  
  Purchase #6 $84.87   11.541%   $94.6648   $94.66   $94.65   $94.70  
  Purchase #7 $17.49   9.173%   $19.0944   $19.09   $19.10   $19.10  
  7 purchase totals = $730.02       $790.0496   $790.04   $790.05   $790.00