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 $58.62   10.837%   $64.9726   $64.97   $64.95   $65.00  
  Purchase #2 $97.98   7.433%   $105.2629   $105.26   $105.25   $105.30  
  Purchase #3 $183.49   5.607%   $193.7783   $193.78   $193.80   $193.80  
  Purchase #4 $79.71   6.170%   $84.6281   $84.63   $84.65   $84.60  
  Purchase #5 $179.87   6.159%   $190.9482   $190.95   $190.95   $190.90  
  Purchase #6 $37.78   3.392%   $39.0615   $39.06   $39.05   $39.10  
  Purchase #7 $250.87   8.521%   $272.2466   $272.25   $272.25   $272.20  
  7 purchase totals = $888.32       $950.8982   $950.90   $950.90   $950.90