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	$39.43	3.839%	$40.9437	$40.94	$40.95	$40.90
Purchase #2	$140.41	12.742%	$158.301	$158.30	$158.30	$158.30
Purchase #3	$169.78	12.594%	$191.1621	$191.16	$191.15	$191.20
Purchase #4	$142.71	13.591%	$162.1057	$162.11	$162.10	$162.10
Purchase #5	$117.65	8.128%	$127.2126	$127.21	$127.20	$127.20
Purchase #6	$246.76	5.560%	$260.4799	$260.48	$260.50	$260.50
Purchase #7	$231.61	10.419%	$255.7414	$255.74	$255.75	$255.70
7 purchase totals =	$1,088.35		$1,195.9464	$1,195.94	$1,195.95	$1,195.90