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	$74.74	10.625%	$82.6811	$82.68	$82.70	$82.70
Purchase #2	$125.44	9.118%	$136.8776	$136.88	$136.90	$136.90
Purchase #3	$250.78	10.700%	$277.6135	$277.61	$277.60	$277.60
Purchase #4	$141.41	12.104%	$158.5263	$158.53	$158.55	$158.50
Purchase #5	$71.27	13.641%	$80.9919	$80.99	$81.00	$81.00
Purchase #6	$249.55	12.149%	$279.8678	$279.87	$279.85	$279.90
Purchase #7	$127.29	12.592%	$143.3184	$143.32	$143.30	$143.30
7 purchase totals =	$1,040.48		$1,159.8766	$1,159.88	$1,159.90	$1,159.90