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 $78.32   10.735%   $86.7277   $86.73   $86.75   $86.70  
  Purchase #2 $92.28   10.105%   $101.6049   $101.60   $101.60   $101.60  
  Purchase #3 $147.71   6.118%   $156.7469   $156.75   $156.75   $156.70  
  Purchase #4 $15.90   5.782%   $16.8193   $16.82   $16.80   $16.80  
  Purchase #5 $13.66   12.171%   $15.3226   $15.32   $15.30   $15.30  
  Purchase #6 $225.55   11.405%   $251.274   $251.27   $251.25   $251.30  
  Purchase #7 $115.43   10.564%   $127.624   $127.62   $127.60   $127.60  
  7 purchase totals = $688.85       $756.1194   $756.11   $756.05   $756.00