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	$20.51	3.473%	$21.2223	$21.22	$21.20	$21.20
Purchase #2	$232.49	6.850%	$248.4156	$248.42	$248.40	$248.40
Purchase #3	$65.62	10.491%	$72.5042	$72.50	$72.50	$72.50
Purchase #4	$125.37	6.333%	$133.3097	$133.31	$133.30	$133.30
Purchase #5	$214.61	4.685%	$224.6645	$224.66	$224.65	$224.70
Purchase #6	$50.57	13.110%	$57.1997	$57.20	$57.20	$57.20
Purchase #7	$198.30	12.142%	$222.3776	$222.38	$222.40	$222.40
7 purchase totals =	$907.47		$979.6936	$979.69	$979.65	$979.70