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	$11.75	12.163%	$13.1792	$13.18	$13.20	$13.20
Purchase #2	$143.43	6.209%	$152.3356	$152.34	$152.35	$152.30
Purchase #3	$14.87	4.485%	$15.5369	$15.54	$15.55	$15.50
Purchase #4	$136.83	3.123%	$141.1032	$141.10	$141.10	$141.10
Purchase #5	$209.83	9.167%	$229.0651	$229.07	$229.05	$229.10
Purchase #6	$41.94	11.199%	$46.6369	$46.64	$46.65	$46.60
Purchase #7	$99.61	6.105%	$105.6912	$105.69	$105.70	$105.70
7 purchase totals =	$658.26		$703.5481	$703.56	$703.60	$703.50