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 $104.37   12.403%   $117.315   $117.32   $117.30   $117.30  
  Purchase #2 $160.35   9.721%   $175.9376   $175.94   $175.95   $175.90  
  Purchase #3 $60.94   9.771%   $66.8944   $66.89   $66.90   $66.90  
  Purchase #4 $97.66   10.344%   $107.762   $107.76   $107.75   $107.80  
  Purchase #5 $247.71   10.626%   $274.0317   $274.03   $274.05   $274.00  
  Purchase #6 $50.62   6.319%   $53.8187   $53.82   $53.80   $53.80  
  Purchase #7 $107.59   13.680%   $122.3083   $122.31   $122.30   $122.30  
  7 purchase totals = $829.24       $918.0677   $918.07   $918.05   $918.00