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	$229.32	7.527%	$246.5809	$246.58	$246.60	$246.60
Purchase #2	$52.51	3.698%	$54.4518	$54.45	$54.45	$54.50
Purchase #3	$127.36	13.351%	$144.3638	$144.36	$144.35	$144.40
Purchase #4	$144.51	13.602%	$164.1663	$164.17	$164.15	$164.20
Purchase #5	$168.46	6.558%	$179.5076	$179.51	$179.50	$179.50
Purchase #6	$142.53	6.532%	$151.8401	$151.84	$151.85	$151.80
Purchase #7	$172.69	4.681%	$180.7736	$180.77	$180.75	$180.80
7 purchase totals =	$1,037.38		$1,121.6841	$1,121.68	$1,121.65	$1,121.80