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 $246.61   7.874%   $266.0281   $266.03   $266.05   $266.00  
  Purchase #2 $239.74   9.683%   $262.954   $262.95   $262.95   $263.00  
  Purchase #3 $67.75   11.763%   $75.7194   $75.72   $75.70   $75.70  
  Purchase #4 $126.42   4.781%   $132.4641   $132.46   $132.45   $132.50  
  Purchase #5 $187.95   6.225%   $199.6499   $199.65   $199.65   $199.60  
  Purchase #6 $29.86   4.198%   $31.1135   $31.11   $31.10   $31.10  
  Purchase #7 $35.80   13.821%   $40.7479   $40.75   $40.75   $40.70  
  7 purchase totals = $934.13       $1,008.6769   $1,008.67   $1,008.65   $1,008.60