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 $58.55   8.403%   $63.47   $63.47   $63.45   $63.50  
  Purchase #2 $37.50   6.403%   $39.9011   $39.90   $39.90   $39.90  
  Purchase #3 $239.78   6.750%   $255.9652   $255.97   $255.95   $256.00  
  Purchase #4 $167.91   3.797%   $174.2855   $174.29   $174.30   $174.30  
  Purchase #5 $44.84   4.161%   $46.7058   $46.71   $46.70   $46.70  
  Purchase #6 $12.72   9.179%   $13.8876   $13.89   $13.90   $13.90  
  Purchase #7 $152.46   13.734%   $173.3989   $173.40   $173.40   $173.40  
  7 purchase totals = $713.76       $767.6141   $767.63   $767.60   $767.70