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	$51.79	13.423%	$58.7418	$58.74	$58.75	$58.70
Purchase #2	$54.46	3.344%	$56.2811	$56.28	$56.30	$56.30
Purchase #3	$43.37	11.807%	$48.4907	$48.49	$48.50	$48.50
Purchase #4	$211.57	10.693%	$234.1932	$234.19	$234.20	$234.20
Purchase #5	$65.72	10.814%	$72.827	$72.83	$72.85	$72.80
Purchase #6	$18.63	6.855%	$19.9071	$19.91	$19.90	$19.90
Purchase #7	$51.70	3.261%	$53.3859	$53.39	$53.40	$53.40
7 purchase totals =	$497.24		$543.8268	$543.83	$543.90	$543.80