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 $244.98   6.539%   $260.9992   $261.00   $261.00   $261.00  
  Purchase #2 $164.36   6.467%   $174.9892   $174.99   $175.00   $175.00  
  Purchase #3 $6.96   8.150%   $7.5272   $7.53   $7.55   $7.50  
  Purchase #4 $54.35   10.849%   $60.2464   $60.25   $60.25   $60.20  
  Purchase #5 $134.73   13.265%   $152.6019   $152.60   $152.60   $152.60  
  Purchase #6 $184.41   9.666%   $202.2351   $202.24   $202.25   $202.20  
  Purchase #7 $42.72   6.422%   $45.4635   $45.46   $45.45   $45.50  
  7 purchase totals = $832.51       $904.0625   $904.07   $904.10   $904.00