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	$54.52	4.175%	$56.7962	$56.80	$56.80	$56.80
Purchase #2	$29.55	5.246%	$31.1002	$31.10	$31.10	$31.10
Purchase #3	$101.62	9.266%	$111.0361	$111.04	$111.05	$111.00
Purchase #4	$163.68	12.873%	$184.7505	$184.75	$184.75	$184.80
Purchase #5	$40.52	5.740%	$42.8458	$42.85	$42.85	$42.80
Purchase #6	$235.48	5.472%	$248.3655	$248.37	$248.35	$248.40
Purchase #7	$219.79	12.667%	$247.6308	$247.63	$247.65	$247.60
7 purchase totals =	$845.16		$922.5251	$922.54	$922.55	$922.50