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	$63.61	12.656%	$71.6605	$71.66	$71.65	$71.70
Purchase #2	$226.42	8.128%	$244.8234	$244.82	$244.80	$244.80
Purchase #3	$140.58	10.259%	$155.0021	$155.00	$155.00	$155.00
Purchase #4	$213.52	7.608%	$229.7646	$229.76	$229.75	$229.80
Purchase #5	$165.29	13.599%	$187.7678	$187.77	$187.75	$187.80
Purchase #6	$168.67	7.209%	$180.8294	$180.83	$180.85	$180.80
Purchase #7	$50.67	6.238%	$53.8308	$53.83	$53.85	$53.80
7 purchase totals =	$1,028.76		$1,123.6786	$1,123.67	$1,123.65	$1,123.70