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	$54.59	3.111%	$56.2883	$56.29	$56.30	$56.30
Purchase #2	$201.39	10.798%	$223.1361	$223.14	$223.15	$223.10
Purchase #3	$129.55	10.232%	$142.8056	$142.81	$142.80	$142.80
Purchase #4	$130.55	7.476%	$140.3099	$140.31	$140.30	$140.30
Purchase #5	$92.87	10.423%	$102.5498	$102.55	$102.55	$102.50
Purchase #6	$92.91	8.680%	$100.9746	$100.97	$100.95	$101.00
Purchase #7	$196.42	7.302%	$210.7626	$210.76	$210.75	$210.80
7 purchase totals =	$898.28		$976.8269	$976.83	$976.80	$976.80