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	$209.57	6.548%	$223.2926	$223.29	$223.30	$223.30
Purchase #2	$22.52	6.821%	$24.0561	$24.06	$24.05	$24.10
Purchase #3	$134.66	6.496%	$143.4075	$143.41	$143.40	$143.40
Purchase #4	$99.54	12.428%	$111.9108	$111.91	$111.90	$111.90
Purchase #5	$162.30	5.492%	$171.2135	$171.21	$171.20	$171.20
Purchase #6	$71.42	4.231%	$74.4418	$74.44	$74.45	$74.40
Purchase #7	$59.58	4.201%	$62.083	$62.08	$62.10	$62.10
7 purchase totals =	$759.59		$810.4053	$810.40	$810.40	$810.40