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	$49.76	10.607%	$55.038	$55.04	$55.05	$55.00
Purchase #2	$189.42	8.103%	$204.7687	$204.77	$204.75	$204.80
Purchase #3	$144.25	4.641%	$150.9446	$150.94	$150.95	$150.90
Purchase #4	$171.25	13.620%	$194.5743	$194.57	$194.55	$194.60
Purchase #5	$54.43	8.854%	$59.2492	$59.25	$59.25	$59.20
Purchase #6	$130.83	9.564%	$143.3426	$143.34	$143.35	$143.30
Purchase #7	$173.30	11.658%	$193.5033	$193.50	$193.50	$193.50
7 purchase totals =	$913.24		$1,001.4207	$1,001.41	$1,001.40	$1,001.30