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 $226.68   6.844%   $242.194   $242.19   $242.20   $242.20  
  Purchase #2 $90.89   7.674%   $97.8649   $97.86   $97.85   $97.90  
  Purchase #3 $43.44   12.401%   $48.827   $48.83   $48.85   $48.80  
  Purchase #4 $117.81   6.473%   $125.4358   $125.44   $125.45   $125.40  
  Purchase #5 $124.56   11.733%   $139.1746   $139.17   $139.15   $139.20  
  Purchase #6 $147.74   6.191%   $156.8866   $156.89   $156.90   $156.90  
  Purchase #7 $141.56   10.815%   $156.8697   $156.87   $156.85   $156.90  
  7 purchase totals = $892.68       $967.2526   $967.25   $967.25   $967.30