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	$54.89	11.819%	$61.3774	$61.38	$61.40	$61.40
Purchase #2	$26.42	5.332%	$27.8287	$27.83	$27.85	$27.80
Purchase #3	$139.88	10.774%	$154.9507	$154.95	$154.95	$155.00
Purchase #4	$120.37	8.335%	$130.4028	$130.40	$130.40	$130.40
Purchase #5	$247.31	6.663%	$263.7883	$263.79	$263.80	$263.80
Purchase #6	$168.32	6.300%	$178.9242	$178.92	$178.90	$178.90
Purchase #7	$19.45	5.594%	$20.538	$20.54	$20.55	$20.50
7 purchase totals =	$776.64		$837.8101	$837.81	$837.85	$837.80