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	$16.79	11.704%	$18.7551	$18.76	$18.75	$18.80
Purchase #2	$229.78	5.694%	$242.8637	$242.86	$242.85	$242.90
Purchase #3	$169.72	8.506%	$184.1564	$184.16	$184.15	$184.20
Purchase #4	$92.90	6.233%	$98.6905	$98.69	$98.70	$98.70
Purchase #5	$229.97	4.419%	$240.1324	$240.13	$240.15	$240.10
Purchase #6	$128.78	10.863%	$142.7694	$142.77	$142.75	$142.80
Purchase #7	$173.53	3.180%	$179.0483	$179.05	$179.05	$179.00
7 purchase totals =	$1,041.47		$1,106.4158	$1,106.42	$1,106.40	$1,106.50