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	$51.38	13.298%	$58.2125	$58.21	$58.20	$58.20
Purchase #2	$57.42	6.764%	$61.3039	$61.30	$61.30	$61.30
Purchase #3	$57.40	8.666%	$62.3743	$62.37	$62.35	$62.40
Purchase #4	$64.87	4.434%	$67.7463	$67.75	$67.75	$67.70
Purchase #5	$117.61	9.445%	$128.7183	$128.72	$128.70	$128.70
Purchase #6	$198.92	5.860%	$210.5767	$210.58	$210.60	$210.60
Purchase #7	$79.71	7.800%	$85.9274	$85.93	$85.95	$85.90
7 purchase totals =	$627.31		$674.8594	$674.86	$674.85	$674.80