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	$80.78	3.369%	$83.5015	$83.50	$83.50	$83.50
Purchase #2	$160.86	5.868%	$170.2993	$170.30	$170.30	$170.30
Purchase #3	$219.25	11.731%	$244.9702	$244.97	$244.95	$245.00
Purchase #4	$91.64	9.510%	$100.355	$100.36	$100.35	$100.40
Purchase #5	$116.37	13.452%	$132.0241	$132.02	$132.00	$132.00
Purchase #6	$123.33	4.495%	$128.8737	$128.87	$128.85	$128.90
Purchase #7	$101.55	9.422%	$111.118	$111.12	$111.10	$111.10
7 purchase totals =	$893.78		$971.1418	$971.14	$971.05	$971.20