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	$244.99	13.532%	$278.142	$278.14	$278.15	$278.10
Purchase #2	$54.63	9.326%	$59.7248	$59.72	$59.70	$59.70
Purchase #3	$75.82	4.653%	$79.3479	$79.35	$79.35	$79.30
Purchase #4	$77.78	5.831%	$82.3154	$82.32	$82.30	$82.30
Purchase #5	$137.36	3.855%	$142.6552	$142.66	$142.65	$142.70
Purchase #6	$179.48	6.551%	$191.2377	$191.24	$191.25	$191.20
Purchase #7	$42.74	6.226%	$45.401	$45.40	$45.40	$45.40
7 purchase totals =	$812.80		$878.8240	$878.83	$878.80	$878.70