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	$111.82	10.452%	$123.5074	$123.51	$123.50	$123.50
Purchase #2	$52.43	10.298%	$57.8292	$57.83	$57.85	$57.80
Purchase #3	$234.66	3.754%	$243.4691	$243.47	$243.45	$243.50
Purchase #4	$101.77	6.483%	$108.3677	$108.37	$108.35	$108.40
Purchase #5	$196.48	11.786%	$219.6371	$219.64	$219.65	$219.60
Purchase #6	$57.40	8.494%	$62.2756	$62.28	$62.30	$62.30
Purchase #7	$51.27	7.515%	$55.1229	$55.12	$55.10	$55.10
7 purchase totals =	$805.83		$870.2090	$870.22	$870.20	$870.20