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	$139.91	7.539%	$150.4578	$150.46	$150.45	$150.50
Purchase #2	$153.64	8.472%	$166.6564	$166.66	$166.65	$166.70
Purchase #3	$59.61	3.747%	$61.8436	$61.84	$61.85	$61.80
Purchase #4	$227.38	12.280%	$255.3023	$255.30	$255.30	$255.30
Purchase #5	$171.43	10.263%	$189.0239	$189.02	$189.00	$189.00
Purchase #6	$64.27	12.367%	$72.2183	$72.22	$72.20	$72.20
Purchase #7	$94.66	5.128%	$99.5142	$99.51	$99.50	$99.50
7 purchase totals =	$910.90		$995.0165	$995.01	$994.95	$995.00