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 $224.73   11.576%   $250.7447   $250.74   $250.75   $250.70  
  Purchase #2 $116.62   13.493%   $132.3555   $132.36   $132.35   $132.40  
  Purchase #3 $5.95   4.628%   $6.2254   $6.23   $6.25   $6.20  
  Purchase #4 $97.26   9.530%   $106.5289   $106.53   $106.55   $106.50  
  Purchase #5 $66.88   5.827%   $70.7771   $70.78   $70.80   $70.80  
  Purchase #6 $111.33   11.508%   $124.1419   $124.14   $124.15   $124.10  
  Purchase #7 $62.86   8.224%   $68.0296   $68.03   $68.05   $68.00  
  7 purchase totals = $685.63       $758.8031   $758.81   $758.90   $758.70