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	$242.59	12.626%	$273.2194	$273.22	$273.20	$273.20
Purchase #2	$24.29	4.525%	$25.3891	$25.39	$25.40	$25.40
Purchase #3	$208.40	3.468%	$215.6273	$215.63	$215.65	$215.60
Purchase #4	$196.90	11.167%	$218.8878	$218.89	$218.90	$218.90
Purchase #5	$181.93	3.258%	$187.8573	$187.86	$187.85	$187.90
Purchase #6	$125.78	5.722%	$132.9771	$132.98	$133.00	$133.00
Purchase #7	$114.43	3.685%	$118.6467	$118.65	$118.65	$118.60
7 purchase totals =	$1,094.32		$1,172.6047	$1,172.62	$1,172.65	$1,172.60