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	$87.37	5.213%	$91.9246	$91.92	$91.90	$91.90
Purchase #2	$91.60	8.541%	$99.4236	$99.42	$99.40	$99.40
Purchase #3	$199.57	12.469%	$224.4544	$224.45	$224.45	$224.50
Purchase #4	$40.57	13.855%	$46.191	$46.19	$46.20	$46.20
Purchase #5	$232.66	6.107%	$246.8685	$246.87	$246.85	$246.90
Purchase #6	$48.96	11.536%	$54.608	$54.61	$54.60	$54.60
Purchase #7	$34.92	6.762%	$37.2813	$37.28	$37.30	$37.30
7 purchase totals =	$735.65		$800.7514	$800.74	$800.70	$800.80