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	$64.33	3.768%	$66.754	$66.75	$66.75	$66.80
Purchase #2	$215.29	10.599%	$238.1086	$238.11	$238.10	$238.10
Purchase #3	$136.31	6.179%	$144.7326	$144.73	$144.75	$144.70
Purchase #4	$144.81	7.616%	$155.8387	$155.84	$155.85	$155.80
Purchase #5	$230.55	3.300%	$238.1582	$238.16	$238.15	$238.20
Purchase #6	$100.62	12.555%	$113.2528	$113.25	$113.25	$113.30
Purchase #7	$178.56	9.158%	$194.9125	$194.91	$194.90	$194.90
7 purchase totals =	$1,070.47		$1,151.7574	$1,151.75	$1,151.75	$1,151.80