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	$231.63	4.150%	$241.2426	$241.24	$241.25	$241.20
Purchase #2	$240.74	13.746%	$273.8321	$273.83	$273.85	$273.80
Purchase #3	$224.65	8.224%	$243.1252	$243.13	$243.15	$243.10
Purchase #4	$242.51	13.771%	$275.9061	$275.91	$275.90	$275.90
Purchase #5	$86.66	4.494%	$90.5545	$90.55	$90.55	$90.60
Purchase #6	$199.90	4.110%	$208.1159	$208.12	$208.10	$208.10
Purchase #7	$217.85	12.714%	$245.5474	$245.55	$245.55	$245.50
7 purchase totals =	$1,443.94		$1,578.3238	$1,578.33	$1,578.35	$1,578.20