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 $55.97   6.450%   $59.5801   $59.58   $59.60   $59.60  
  Purchase #2 $232.67   5.723%   $245.9857   $245.99   $246.00   $246.00  
  Purchase #3 $118.63   4.310%   $123.743   $123.74   $123.75   $123.70  
  Purchase #4 $104.94   3.197%   $108.2949   $108.29   $108.30   $108.30  
  Purchase #5 $6.70   7.125%   $7.1774   $7.18   $7.20   $7.20  
  Purchase #6 $175.80   13.755%   $199.9813   $199.98   $200.00   $200.00  
  Purchase #7 $192.68   10.129%   $212.1966   $212.20   $212.20   $212.20  
  7 purchase totals = $887.39       $956.9590   $956.96   $957.05   $957.00