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	$25.41	7.335%	$27.2738	$27.27	$27.25	$27.30
Purchase #2	$62.90	4.552%	$65.7632	$65.76	$65.75	$65.80
Purchase #3	$185.39	7.715%	$199.6928	$199.69	$199.70	$199.70
Purchase #4	$243.87	4.297%	$254.3491	$254.35	$254.35	$254.30
Purchase #5	$150.45	12.727%	$169.5978	$169.60	$169.60	$169.60
Purchase #6	$236.87	4.376%	$247.2354	$247.24	$247.25	$247.20
Purchase #7	$32.58	13.847%	$37.0914	$37.09	$37.10	$37.10
7 purchase totals =	$937.47		$1,001.0035	$1,001.00	$1,001.00	$1,001.00