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 $67.88   6.102%   $72.022   $72.02   $72.00   $72.00  
  Purchase #2 $50.63   3.394%   $52.3484   $52.35   $52.35   $52.30  
  Purchase #3 $6.41   4.173%   $6.6775   $6.68   $6.70   $6.70  
  Purchase #4 $143.70   6.544%   $153.1037   $153.10   $153.10   $153.10  
  Purchase #5 $107.99   11.547%   $120.4596   $120.46   $120.45   $120.50  
  Purchase #6 $84.43   13.259%   $95.6246   $95.62   $95.60   $95.60  
  Purchase #7 $227.74   12.728%   $256.7267   $256.73   $256.75   $256.70  
  7 purchase totals = $688.78       $756.9625   $756.96   $756.95   $756.90