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 $57.71   8.268%   $62.4815   $62.48   $62.50   $62.50  
  Purchase #2 $162.69   8.458%   $176.4503   $176.45   $176.45   $176.50  
  Purchase #3 $50.83   8.364%   $55.0814   $55.08   $55.10   $55.10  
  Purchase #4 $32.40   6.253%   $34.426   $34.43   $34.45   $34.40  
  Purchase #5 $244.71   5.428%   $257.9929   $257.99   $258.00   $258.00  
  Purchase #6 $106.37   9.472%   $116.4454   $116.45   $116.45   $116.40  
  Purchase #7 $19.59   5.714%   $20.7094   $20.71   $20.70   $20.70  
  7 purchase totals = $674.30       $723.5869   $723.59   $723.65   $723.60