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 $245.36   9.485%   $268.6324   $268.63   $268.65   $268.60  
  Purchase #2 $126.58   13.254%   $143.3569   $143.36   $143.35   $143.40  
  Purchase #3 $156.45   3.334%   $161.666   $161.67   $161.65   $161.70  
  Purchase #4 $100.29   12.771%   $113.098   $113.10   $113.10   $113.10  
  Purchase #5 $66.78   3.773%   $69.2996   $69.30   $69.30   $69.30  
  Purchase #6 $17.47   5.354%   $18.4053   $18.41   $18.40   $18.40  
  Purchase #7 $233.61   12.550%   $262.9281   $262.93   $262.95   $262.90  
  7 purchase totals = $946.54       $1,037.3863   $1,037.40   $1,037.40   $1,037.40