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	$226.70	9.711%	$248.7148	$248.71	$248.70	$248.70
Purchase #2	$38.73	4.688%	$40.5457	$40.55	$40.55	$40.50
Purchase #3	$137.43	3.113%	$141.7082	$141.71	$141.70	$141.70
Purchase #4	$48.43	13.403%	$54.9211	$54.92	$54.90	$54.90
Purchase #5	$16.49	11.485%	$18.3839	$18.38	$18.40	$18.40
Purchase #6	$80.60	10.334%	$88.9292	$88.93	$88.95	$88.90
Purchase #7	$186.32	7.466%	$200.2307	$200.23	$200.25	$200.20
7 purchase totals =	$734.70		$793.4336	$793.43	$793.45	$793.30