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	$38.62	4.342%	$40.2969	$40.30	$40.30	$40.30
Purchase #2	$149.76	13.399%	$169.8263	$169.83	$169.85	$169.80
Purchase #3	$214.70	5.472%	$226.4484	$226.45	$226.45	$226.40
Purchase #4	$188.42	12.463%	$211.9028	$211.90	$211.90	$211.90
Purchase #5	$200.61	7.316%	$215.2866	$215.29	$215.30	$215.30
Purchase #6	$151.56	12.448%	$170.4262	$170.43	$170.45	$170.40
Purchase #7	$10.33	5.197%	$10.8669	$10.87	$10.85	$10.90
7 purchase totals =	$954.00		$1,045.0541	$1,045.07	$1,045.10	$1,045.00