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	$153.67	3.872%	$159.6201	$159.62	$159.60	$159.60
Purchase #2	$26.33	5.449%	$27.7647	$27.76	$27.75	$27.80
Purchase #3	$249.66	3.505%	$258.4106	$258.41	$258.40	$258.40
Purchase #4	$91.94	13.604%	$104.4475	$104.45	$104.45	$104.40
Purchase #5	$116.62	10.335%	$128.6727	$128.67	$128.65	$128.70
Purchase #6	$118.51	10.667%	$131.1515	$131.15	$131.15	$131.20
Purchase #7	$185.54	7.607%	$199.654	$199.65	$199.65	$199.70
7 purchase totals =	$942.27		$1,009.7211	$1,009.71	$1,009.65	$1,009.80