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	$199.83	12.233%	$224.2752	$224.28	$224.30	$224.30
Purchase #2	$100.62	11.155%	$111.8442	$111.84	$111.85	$111.80
Purchase #3	$147.51	12.853%	$166.4695	$166.47	$166.45	$166.50
Purchase #4	$97.40	4.440%	$101.7246	$101.72	$101.70	$101.70
Purchase #5	$81.89	8.818%	$89.1111	$89.11	$89.10	$89.10
Purchase #6	$201.99	13.685%	$229.6323	$229.63	$229.65	$229.60
Purchase #7	$182.78	3.142%	$188.5229	$188.52	$188.50	$188.50
7 purchase totals =	$1,012.02		$1,111.5798	$1,111.57	$1,111.55	$1,111.50