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	$67.34	6.228%	$71.5339	$71.53	$71.55	$71.50
Purchase #2	$63.56	11.157%	$70.6514	$70.65	$70.65	$70.70
Purchase #3	$104.57	6.466%	$111.3315	$111.33	$111.35	$111.30
Purchase #4	$56.42	13.696%	$64.1473	$64.15	$64.15	$64.10
Purchase #5	$29.52	10.451%	$32.6051	$32.61	$32.60	$32.60
Purchase #6	$53.70	7.576%	$57.7683	$57.77	$57.75	$57.80
Purchase #7	$210.40	11.341%	$234.2615	$234.26	$234.25	$234.30
7 purchase totals =	$585.51		$642.2990	$642.30	$642.30	$642.30