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 $107.57   10.645%   $119.0208   $119.02   $119.00   $119.00  
  Purchase #2 $151.60   4.777%   $158.8419   $158.84   $158.85   $158.80  
  Purchase #3 $148.87   9.539%   $163.0707   $163.07   $163.05   $163.10  
  Purchase #4 $244.89   6.533%   $260.8887   $260.89   $260.90   $260.90  
  Purchase #5 $180.85   10.481%   $199.8049   $199.80   $199.80   $199.80  
  Purchase #6 $87.32   7.234%   $93.6367   $93.64   $93.65   $93.60  
  Purchase #7 $212.34   12.384%   $238.6362   $238.64   $238.65   $238.60  
  7 purchase totals = $1,133.44       $1,233.8999   $1,233.90   $1,233.90   $1,233.80