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 $62.32   5.874%   $65.9807   $65.98   $66.00   $66.00  
  Purchase #2 $153.77   9.460%   $168.3166   $168.32   $168.30   $168.30  
  Purchase #3 $103.60   11.222%   $115.226   $115.23   $115.25   $115.20  
  Purchase #4 $124.52   10.516%   $137.6145   $137.61   $137.60   $137.60  
  Purchase #5 $62.95   11.676%   $70.3   $70.30   $70.30   $70.30  
  Purchase #6 $103.88   3.398%   $107.4098   $107.41   $107.40   $107.40  
  Purchase #7 $137.54   10.486%   $151.9624   $151.96   $151.95   $152.00  
  7 purchase totals = $748.58       $816.8100   $816.81   $816.80   $816.80