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	$67.88	4.628%	$71.0215	$71.02	$71.00	$71.00
Purchase #2	$37.97	5.435%	$40.0337	$40.03	$40.05	$40.00
Purchase #3	$83.60	13.846%	$95.1753	$95.18	$95.20	$95.20
Purchase #4	$182.96	6.195%	$194.2944	$194.29	$194.30	$194.30
Purchase #5	$89.42	12.575%	$100.6646	$100.66	$100.65	$100.70
Purchase #6	$156.74	9.738%	$172.0033	$172.00	$172.00	$172.00
Purchase #7	$171.59	10.450%	$189.5212	$189.52	$189.50	$189.50
7 purchase totals =	$790.16		$862.7140	$862.70	$862.70	$862.70