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	$234.56	10.534%	$259.2686	$259.27	$259.25	$259.30
Purchase #2	$12.85	11.349%	$14.3083	$14.31	$14.30	$14.30
Purchase #3	$144.64	10.276%	$159.5032	$159.50	$159.50	$159.50
Purchase #4	$241.88	13.760%	$275.1627	$275.16	$275.15	$275.20
Purchase #5	$163.29	12.850%	$184.2728	$184.27	$184.25	$184.30
Purchase #6	$10.72	13.356%	$12.1518	$12.15	$12.15	$12.20
Purchase #7	$123.59	10.402%	$136.4458	$136.45	$136.45	$136.40
7 purchase totals =	$931.53		$1,041.1132	$1,041.11	$1,041.05	$1,041.20