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 $26.29   13.853%   $29.932   $29.93   $29.95   $29.90  
  Purchase #2 $88.50   10.341%   $97.6518   $97.65   $97.65   $97.70  
  Purchase #3 $50.73   9.481%   $55.5397   $55.54   $55.55   $55.50  
  Purchase #4 $56.37   11.421%   $62.808   $62.81   $62.80   $62.80  
  Purchase #5 $53.87   6.233%   $57.2277   $57.23   $57.25   $57.20  
  Purchase #6 $196.46   5.188%   $206.6523   $206.65   $206.65   $206.70  
  Purchase #7 $229.26   3.132%   $236.4404   $236.44   $236.45   $236.40  
  7 purchase totals = $701.48       $746.2519   $746.25   $746.30   $746.20