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	$38.26	9.361%	$41.8415	$41.84	$41.85	$41.80
Purchase #2	$134.96	13.294%	$152.9016	$152.90	$152.90	$152.90
Purchase #3	$42.79	13.494%	$48.5641	$48.56	$48.55	$48.60
Purchase #4	$209.64	9.317%	$229.1722	$229.17	$229.15	$229.20
Purchase #5	$83.27	10.349%	$91.8876	$91.89	$91.90	$91.90
Purchase #6	$79.96	10.422%	$88.2934	$88.29	$88.30	$88.30
Purchase #7	$184.49	3.303%	$190.5837	$190.58	$190.60	$190.60
7 purchase totals =	$773.37		$843.2441	$843.23	$843.25	$843.30