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 $179.45   13.283%   $203.2863   $203.29   $203.30   $203.30  
  Purchase #2 $212.73   7.746%   $229.2081   $229.21   $229.20   $229.20  
  Purchase #3 $116.55   6.468%   $124.0885   $124.09   $124.10   $124.10  
  Purchase #4 $39.62   4.692%   $41.479   $41.48   $41.50   $41.50  
  Purchase #5 $105.42   6.817%   $112.6065   $112.61   $112.60   $112.60  
  Purchase #6 $41.86   4.783%   $43.8622   $43.86   $43.85   $43.90  
  Purchase #7 $68.36   8.322%   $74.0489   $74.05   $74.05   $74.00  
  7 purchase totals = $763.99       $828.5795   $828.59   $828.60   $828.60