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 $54.63   7.417%   $58.6819   $58.68   $58.70   $58.70  
  Purchase #2 $88.80   5.756%   $93.9113   $93.91   $93.90   $93.90  
  Purchase #3 $113.29   9.150%   $123.656   $123.66   $123.65   $123.70  
  Purchase #4 $85.34   7.269%   $91.5434   $91.54   $91.55   $91.50  
  Purchase #5 $185.61   13.536%   $210.7342   $210.73   $210.75   $210.70  
  Purchase #6 $41.81   4.714%   $43.7809   $43.78   $43.80   $43.80  
  Purchase #7 $144.88   9.257%   $158.2915   $158.29   $158.30   $158.30  
  7 purchase totals = $714.36       $780.5992   $780.59   $780.65   $780.60