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	$17.61	3.114%	$18.1584	$18.16	$18.15	$18.20
Purchase #2	$85.54	12.860%	$96.5404	$96.54	$96.55	$96.50
Purchase #3	$212.75	3.185%	$219.5261	$219.53	$219.55	$219.50
Purchase #4	$218.72	10.358%	$241.375	$241.38	$241.40	$241.40
Purchase #5	$130.72	6.598%	$139.3449	$139.34	$139.35	$139.30
Purchase #6	$206.96	11.177%	$230.0919	$230.09	$230.10	$230.10
Purchase #7	$209.35	11.414%	$233.2452	$233.25	$233.25	$233.20
7 purchase totals =	$1,081.65		$1,178.2819	$1,178.29	$1,178.35	$1,178.20