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 $235.25   11.578%   $262.4872   $262.49   $262.50   $262.50  
  Purchase #2 $231.60   3.562%   $239.8496   $239.85   $239.85   $239.80  
  Purchase #3 $157.30   6.726%   $167.88   $167.88   $167.90   $167.90  
  Purchase #4 $65.36   6.854%   $69.8398   $69.84   $69.85   $69.80  
  Purchase #5 $112.57   11.316%   $125.3084   $125.31   $125.30   $125.30  
  Purchase #6 $66.66   11.635%   $74.4159   $74.42   $74.40   $74.40  
  Purchase #7 $114.47   12.856%   $129.1863   $129.19   $129.20   $129.20  
  7 purchase totals = $983.21       $1,068.9672   $1,068.98   $1,069.00   $1,068.90