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	$64.73	10.483%	$71.5156	$71.52	$71.50	$71.50
Purchase #2	$62.77	12.563%	$70.6558	$70.66	$70.65	$70.70
Purchase #3	$125.85	9.481%	$137.7818	$137.78	$137.80	$137.80
Purchase #4	$91.52	10.803%	$101.4069	$101.41	$101.40	$101.40
Purchase #5	$199.33	11.418%	$222.0895	$222.09	$222.10	$222.10
Purchase #6	$235.42	10.204%	$259.4423	$259.44	$259.45	$259.40
Purchase #7	$131.46	4.527%	$137.4112	$137.41	$137.40	$137.40
7 purchase totals =	$911.08		$1,000.3031	$1,000.31	$1,000.30	$1,000.30