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	$8.89	13.280%	$10.0706	$10.07	$10.05	$10.10
Purchase #2	$65.89	7.480%	$70.8186	$70.82	$70.80	$70.80
Purchase #3	$167.95	7.140%	$179.9416	$179.94	$179.95	$179.90
Purchase #4	$67.73	9.674%	$74.2822	$74.28	$74.30	$74.30
Purchase #5	$141.25	7.667%	$152.0796	$152.08	$152.10	$152.10
Purchase #6	$169.64	5.862%	$179.5843	$179.58	$179.60	$179.60
Purchase #7	$17.56	6.590%	$18.7172	$18.72	$18.70	$18.70
7 purchase totals =	$638.91		$685.4941	$685.49	$685.50	$685.50