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 $44.55   13.571%   $50.5959   $50.60   $50.60   $50.60  
  Purchase #2 $231.71   9.526%   $253.7827   $253.78   $253.80   $253.80  
  Purchase #3 $60.48   6.193%   $64.2255   $64.23   $64.25   $64.20  
  Purchase #4 $54.58   8.433%   $59.1827   $59.18   $59.20   $59.20  
  Purchase #5 $51.84   6.270%   $55.0904   $55.09   $55.10   $55.10  
  Purchase #6 $6.73   6.761%   $7.185   $7.19   $7.20   $7.20  
  Purchase #7 $201.42   6.649%   $214.8124   $214.81   $214.80   $214.80  
  7 purchase totals = $651.31       $704.8746   $704.88   $704.95   $704.90