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	$95.87	3.400%	$99.1296	$99.13	$99.15	$99.10
Purchase #2	$176.86	13.158%	$200.1312	$200.13	$200.15	$200.10
Purchase #3	$162.77	5.514%	$171.7451	$171.75	$171.75	$171.70
Purchase #4	$115.29	10.613%	$127.5257	$127.53	$127.55	$127.50
Purchase #5	$118.33	4.557%	$123.7223	$123.72	$123.70	$123.70
Purchase #6	$27.60	12.191%	$30.9647	$30.96	$30.95	$31.00
Purchase #7	$9.64	4.736%	$10.0966	$10.10	$10.10	$10.10
7 purchase totals =	$706.36		$763.3152	$763.32	$763.35	$763.20