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	$123.40	10.427%	$136.2669	$136.27	$136.25	$136.30
Purchase #2	$236.26	8.524%	$256.3988	$256.40	$256.40	$256.40
Purchase #3	$103.27	7.727%	$111.2497	$111.25	$111.25	$111.20
Purchase #4	$76.99	7.181%	$82.5187	$82.52	$82.50	$82.50
Purchase #5	$112.62	8.232%	$121.8909	$121.89	$121.90	$121.90
Purchase #6	$230.91	5.837%	$244.3882	$244.39	$244.40	$244.40
Purchase #7	$164.53	6.489%	$175.2064	$175.21	$175.20	$175.20
7 purchase totals =	$1,047.98		$1,127.9196	$1,127.93	$1,127.90	$1,127.90