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	$121.37	7.262%	$130.1839	$130.18	$130.20	$130.20
Purchase #2	$85.40	4.104%	$88.9048	$88.90	$88.90	$88.90
Purchase #3	$111.54	10.530%	$123.2852	$123.29	$123.30	$123.30
Purchase #4	$242.95	8.319%	$263.161	$263.16	$263.15	$263.20
Purchase #5	$197.26	11.163%	$219.2801	$219.28	$219.30	$219.30
Purchase #6	$49.67	5.855%	$52.5782	$52.58	$52.60	$52.60
Purchase #7	$134.42	6.249%	$142.8199	$142.82	$142.80	$142.80
7 purchase totals =	$942.61		$1,020.2131	$1,020.21	$1,020.25	$1,020.30