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	$152.40	11.166%	$169.417	$169.42	$169.40	$169.40
Purchase #2	$134.58	6.560%	$143.4084	$143.41	$143.40	$143.40
Purchase #3	$30.43	8.490%	$33.0135	$33.01	$33.00	$33.00
Purchase #4	$149.91	7.334%	$160.9044	$160.90	$160.90	$160.90
Purchase #5	$244.47	4.152%	$254.6204	$254.62	$254.60	$254.60
Purchase #6	$219.85	4.481%	$229.7015	$229.70	$229.70	$229.70
Purchase #7	$71.86	12.246%	$80.66	$80.66	$80.65	$80.70
7 purchase totals =	$1,003.50		$1,071.7252	$1,071.72	$1,071.65	$1,071.70