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	$84.35	8.192%	$91.26	$91.26	$91.25	$91.30
Purchase #2	$166.62	11.340%	$185.5147	$185.51	$185.50	$185.50
Purchase #3	$108.70	11.147%	$120.8168	$120.82	$120.80	$120.80
Purchase #4	$115.26	11.807%	$128.8687	$128.87	$128.85	$128.90
Purchase #5	$205.51	5.598%	$217.0144	$217.01	$217.00	$217.00
Purchase #6	$54.33	13.776%	$61.8145	$61.81	$61.80	$61.80
Purchase #7	$190.69	4.493%	$199.2577	$199.26	$199.25	$199.30
7 purchase totals =	$925.46		$1,004.5468	$1,004.54	$1,004.45	$1,004.60