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	$77.67	9.721%	$85.2203	$85.22	$85.20	$85.20
Purchase #2	$170.40	5.336%	$179.4925	$179.49	$179.50	$179.50
Purchase #3	$166.47	4.675%	$174.2525	$174.25	$174.25	$174.30
Purchase #4	$55.99	10.714%	$61.9888	$61.99	$62.00	$62.00
Purchase #5	$46.54	12.657%	$52.4306	$52.43	$52.45	$52.40
Purchase #6	$155.58	9.607%	$170.5266	$170.53	$170.55	$170.50
Purchase #7	$75.37	4.231%	$78.5589	$78.56	$78.55	$78.60
7 purchase totals =	$748.02		$802.4702	$802.47	$802.50	$802.50