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 $246.30   6.704%   $262.812   $262.81   $262.80   $262.80  
  Purchase #2 $241.36   10.447%   $266.5749   $266.57   $266.55   $266.60  
  Purchase #3 $71.51   5.198%   $75.2271   $75.23   $75.25   $75.20  
  Purchase #4 $78.90   13.867%   $89.8411   $89.84   $89.85   $89.80  
  Purchase #5 $79.47   6.152%   $84.359   $84.36   $84.35   $84.40  
  Purchase #6 $15.77   5.433%   $16.6268   $16.63   $16.65   $16.60  
  Purchase #7 $109.99   10.353%   $121.3773   $121.38   $121.40   $121.40  
  7 purchase totals = $843.30       $916.8182   $916.82   $916.85   $916.80