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 $9.50   6.434%   $10.1112   $10.11   $10.10   $10.10  
  Purchase #2 $199.29   5.433%   $210.1174   $210.12   $210.10   $210.10  
  Purchase #3 $7.53   11.549%   $8.3996   $8.40   $8.40   $8.40  
  Purchase #4 $29.44   5.246%   $30.9844   $30.98   $31.00   $31.00  
  Purchase #5 $121.94   6.848%   $130.2905   $130.29   $130.30   $130.30  
  Purchase #6 $13.60   3.420%   $14.0651   $14.07   $14.05   $14.10  
  Purchase #7 $128.33   6.400%   $136.5431   $136.54   $136.55   $136.50  
  7 purchase totals = $509.63       $540.5113   $540.51   $540.50   $540.50