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 $229.35   7.559%   $246.6866   $246.69   $246.70   $246.70  
  Purchase #2 $18.82   11.145%   $20.9175   $20.92   $20.90   $20.90  
  Purchase #3 $82.58   9.431%   $90.3681   $90.37   $90.35   $90.40  
  Purchase #4 $175.72   6.580%   $187.2824   $187.28   $187.30   $187.30  
  Purchase #5 $86.48   13.200%   $97.8954   $97.90   $97.90   $97.90  
  Purchase #6 $73.37   4.650%   $76.7817   $76.78   $76.80   $76.80  
  Purchase #7 $28.53   6.389%   $30.3528   $30.35   $30.35   $30.40  
  7 purchase totals = $694.85       $750.2845   $750.29   $750.30   $750.40