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 $55.36   12.420%   $62.2357   $62.24   $62.25   $62.20  
  Purchase #2 $70.92   6.366%   $75.4348   $75.43   $75.45   $75.40  
  Purchase #3 $158.91   10.624%   $175.7926   $175.79   $175.80   $175.80  
  Purchase #4 $94.66   3.131%   $97.6238   $97.62   $97.60   $97.60  
  Purchase #5 $97.67   8.371%   $105.846   $105.85   $105.85   $105.80  
  Purchase #6 $160.40   6.253%   $170.4298   $170.43   $170.45   $170.40  
  Purchase #7 $202.34   11.493%   $225.5949   $225.59   $225.60   $225.60  
  7 purchase totals = $840.26       $912.9576   $912.95   $913.00   $912.80