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	$84.88	5.451%	$89.5068	$89.51	$89.50	$89.50
Purchase #2	$44.42	12.124%	$49.8055	$49.81	$49.80	$49.80
Purchase #3	$243.72	11.465%	$271.6625	$271.66	$271.65	$271.70
Purchase #4	$104.39	6.538%	$111.215	$111.22	$111.20	$111.20
Purchase #5	$203.77	11.462%	$227.1261	$227.13	$227.15	$227.10
Purchase #6	$190.33	7.465%	$204.5381	$204.54	$204.55	$204.50
Purchase #7	$180.71	8.152%	$195.4415	$195.44	$195.45	$195.40
7 purchase totals =	$1,052.22		$1,149.2955	$1,149.31	$1,149.30	$1,149.20