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	$38.45	13.396%	$43.6008	$43.60	$43.60	$43.60
Purchase #2	$130.78	6.551%	$139.3474	$139.35	$139.35	$139.30
Purchase #3	$152.29	11.700%	$170.1079	$170.11	$170.10	$170.10
Purchase #4	$46.38	8.308%	$50.2333	$50.23	$50.25	$50.20
Purchase #5	$211.46	10.637%	$233.953	$233.95	$233.95	$234.00
Purchase #6	$39.76	7.594%	$42.7794	$42.78	$42.80	$42.80
Purchase #7	$16.43	6.364%	$17.4756	$17.48	$17.50	$17.50
7 purchase totals =	$635.55		$697.4974	$697.50	$697.55	$697.50