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 $36.77   13.161%   $41.6093   $41.61   $41.60   $41.60  
  Purchase #2 $141.86   7.799%   $152.9237   $152.92   $152.90   $152.90  
  Purchase #3 $123.67   7.475%   $132.9143   $132.91   $132.90   $132.90  
  Purchase #4 $81.88   11.813%   $91.5525   $91.55   $91.55   $91.60  
  Purchase #5 $110.42   5.531%   $116.5273   $116.53   $116.55   $116.50  
  Purchase #6 $119.57   9.222%   $130.5967   $130.60   $130.60   $130.60  
  Purchase #7 $9.32   4.204%   $9.7118   $9.71   $9.70   $9.70  
  7 purchase totals = $623.49       $675.8356   $675.83   $675.80   $675.80