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 $71.67   7.314%   $76.9119   $76.91   $76.90   $76.90  
  Purchase #2 $76.68   8.597%   $83.2722   $83.27   $83.25   $83.30  
  Purchase #3 $168.98   4.615%   $176.7784   $176.78   $176.80   $176.80  
  Purchase #4 $101.86   6.259%   $108.2354   $108.24   $108.25   $108.20  
  Purchase #5 $5.26   7.399%   $5.6492   $5.65   $5.65   $5.60  
  Purchase #6 $9.28   4.654%   $9.7119   $9.71   $9.70   $9.70  
  Purchase #7 $240.71   5.250%   $253.3473   $253.35   $253.35   $253.30  
  7 purchase totals = $674.44       $713.9063   $713.91   $713.90   $713.80