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	$7.40	9.460%	$8.1	$8.10	$8.10	$8.10
Purchase #2	$84.42	7.306%	$90.5877	$90.59	$90.60	$90.60
Purchase #3	$56.98	4.380%	$59.4757	$59.48	$59.50	$59.50
Purchase #4	$74.46	11.781%	$83.2321	$83.23	$83.25	$83.20
Purchase #5	$170.46	4.422%	$177.9977	$178.00	$178.00	$178.00
Purchase #6	$154.41	6.406%	$164.3015	$164.30	$164.30	$164.30
Purchase #7	$34.63	13.700%	$39.3743	$39.37	$39.35	$39.40
7 purchase totals =	$582.76		$623.0690	$623.07	$623.10	$623.10