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	$49.53	11.809%	$55.379	$55.38	$55.40	$55.40
Purchase #2	$136.72	12.297%	$153.5325	$153.53	$153.55	$153.50
Purchase #3	$134.85	12.613%	$151.8586	$151.86	$151.85	$151.90
Purchase #4	$57.96	6.559%	$61.7616	$61.76	$61.75	$61.80
Purchase #5	$247.46	7.821%	$266.8138	$266.81	$266.80	$266.80
Purchase #6	$92.63	8.675%	$100.6657	$100.67	$100.65	$100.70
Purchase #7	$85.66	12.751%	$96.5825	$96.58	$96.60	$96.60
7 purchase totals =	$804.81		$886.5937	$886.59	$886.60	$886.70