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 $242.30   10.318%   $267.3005   $267.30   $267.30   $267.30  
  Purchase #2 $116.27   7.361%   $124.8286   $124.83   $124.85   $124.80  
  Purchase #3 $175.37   9.159%   $191.4321   $191.43   $191.45   $191.40  
  Purchase #4 $131.39   11.262%   $146.1871   $146.19   $146.20   $146.20  
  Purchase #5 $118.94   5.345%   $125.2973   $125.30   $125.30   $125.30  
  Purchase #6 $120.36   11.612%   $134.3362   $134.34   $134.35   $134.30  
  Purchase #7 $227.99   7.384%   $244.8248   $244.82   $244.80   $244.80  
  7 purchase totals = $1,132.62       $1,234.2066   $1,234.21   $1,234.25   $1,234.10