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 $246.58   8.779%   $268.2273   $268.23   $268.25   $268.20  
  Purchase #2 $124.98   8.440%   $135.5283   $135.53   $135.55   $135.50  
  Purchase #3 $150.65   6.317%   $160.1666   $160.17   $160.15   $160.20  
  Purchase #4 $82.91   10.512%   $91.6255   $91.63   $91.65   $91.60  
  Purchase #5 $195.41   13.256%   $221.3135   $221.31   $221.30   $221.30  
  Purchase #6 $134.64   7.322%   $144.4983   $144.50   $144.50   $144.50  
  Purchase #7 $206.51   4.569%   $215.9454   $215.95   $215.95   $215.90  
  7 purchase totals = $1,141.68       $1,237.3049   $1,237.32   $1,237.35   $1,237.20