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 $57.50   9.448%   $62.9326   $62.93   $62.95   $62.90  
  Purchase #2 $224.37   12.472%   $252.3534   $252.35   $252.35   $252.40  
  Purchase #3 $244.53   4.778%   $256.2136   $256.21   $256.20   $256.20  
  Purchase #4 $161.79   12.580%   $182.1432   $182.14   $182.15   $182.10  
  Purchase #5 $181.48   7.289%   $194.7081   $194.71   $194.70   $194.70  
  Purchase #6 $23.26   8.644%   $25.2706   $25.27   $25.25   $25.30  
  Purchase #7 $71.81   4.141%   $74.7837   $74.78   $74.80   $74.80  
  7 purchase totals = $964.74       $1,048.4052   $1,048.39   $1,048.40   $1,048.40