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 $18.30   6.458%   $19.4818   $19.48   $19.50   $19.50  
  Purchase #2 $214.89   13.649%   $244.2203   $244.22   $244.20   $244.20  
  Purchase #3 $245.29   9.198%   $267.8518   $267.85   $267.85   $267.90  
  Purchase #4 $53.93   7.382%   $57.9111   $57.91   $57.90   $57.90  
  Purchase #5 $180.45   5.185%   $189.8063   $189.81   $189.80   $189.80  
  Purchase #6 $153.36   5.243%   $161.4007   $161.40   $161.40   $161.40  
  Purchase #7 $6.92   11.185%   $7.694   $7.69   $7.70   $7.70  
  7 purchase totals = $873.14       $948.3660   $948.36   $948.35   $948.40