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	$112.36	7.311%	$120.5746	$120.57	$120.55	$120.60
Purchase #2	$53.78	10.733%	$59.5522	$59.55	$59.55	$59.60
Purchase #3	$174.41	12.823%	$196.7746	$196.77	$196.75	$196.80
Purchase #4	$127.29	13.433%	$144.3889	$144.39	$144.40	$144.40
Purchase #5	$202.42	7.767%	$218.142	$218.14	$218.15	$218.10
Purchase #6	$156.45	9.239%	$170.9044	$170.90	$170.90	$170.90
Purchase #7	$202.68	3.274%	$209.3157	$209.32	$209.30	$209.30
7 purchase totals =	$1,029.39		$1,119.6524	$1,119.64	$1,119.60	$1,119.70