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 $146.89   3.704%   $152.3308   $152.33   $152.35   $152.30  
  Purchase #2 $245.28   8.830%   $266.9382   $266.94   $266.95   $266.90  
  Purchase #3 $125.83   10.576%   $139.1378   $139.14   $139.15   $139.10  
  Purchase #4 $23.61   13.111%   $26.7055   $26.71   $26.70   $26.70  
  Purchase #5 $238.98   4.738%   $250.3029   $250.30   $250.30   $250.30  
  Purchase #6 $156.38   11.383%   $174.1807   $174.18   $174.20   $174.20  
  Purchase #7 $239.99   11.413%   $267.3801   $267.38   $267.40   $267.40  
  7 purchase totals = $1,176.96       $1,276.9760   $1,276.98   $1,277.05   $1,276.90