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	$230.51	9.272%	$251.8829	$251.88	$251.90	$251.90
Purchase #2	$234.89	3.380%	$242.8293	$242.83	$242.85	$242.80
Purchase #3	$213.96	8.106%	$231.3036	$231.30	$231.30	$231.30
Purchase #4	$111.80	6.707%	$119.2984	$119.30	$119.30	$119.30
Purchase #5	$208.61	5.306%	$219.6788	$219.68	$219.70	$219.70
Purchase #6	$18.78	9.221%	$20.5117	$20.51	$20.50	$20.50
Purchase #7	$81.60	10.607%	$90.2553	$90.26	$90.25	$90.30
7 purchase totals =	$1,100.15		$1,175.7600	$1,175.76	$1,175.80	$1,175.80