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 $200.64   3.157%   $206.9742   $206.97   $206.95   $207.00  
  Purchase #2 $16.99   13.809%   $19.3361   $19.34   $19.35   $19.30  
  Purchase #3 $59.84   6.343%   $63.6357   $63.64   $63.65   $63.60  
  Purchase #4 $74.80   4.762%   $78.362   $78.36   $78.35   $78.40  
  Purchase #5 $85.76   13.373%   $97.2287   $97.23   $97.25   $97.20  
  Purchase #6 $43.62   9.181%   $47.6248   $47.62   $47.60   $47.60  
  Purchase #7 $119.82   4.129%   $124.7674   $124.77   $124.75   $124.80  
  7 purchase totals = $601.47       $637.9289   $637.93   $637.90   $637.90