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 $237.26   9.867%   $260.6704   $260.67   $260.65   $260.70  
  Purchase #2 $121.36   10.139%   $133.6647   $133.66   $133.65   $133.70  
  Purchase #3 $60.90   13.722%   $69.2567   $69.26   $69.25   $69.30  
  Purchase #4 $215.81   10.548%   $238.5736   $238.57   $238.55   $238.60  
  Purchase #5 $95.33   12.561%   $107.3044   $107.30   $107.30   $107.30  
  Purchase #6 $128.96   6.346%   $137.1438   $137.14   $137.15   $137.10  
  Purchase #7 $69.83   10.127%   $76.9017   $76.90   $76.90   $76.90  
  7 purchase totals = $929.45       $1,023.5153   $1,023.50   $1,023.45   $1,023.60