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	$122.68	6.237%	$130.3316	$130.33	$130.35	$130.30
Purchase #2	$202.25	8.479%	$219.3988	$219.40	$219.40	$219.40
Purchase #3	$196.46	11.526%	$219.104	$219.10	$219.10	$219.10
Purchase #4	$189.58	4.180%	$197.5044	$197.50	$197.50	$197.50
Purchase #5	$55.43	3.345%	$57.2841	$57.28	$57.30	$57.30
Purchase #6	$47.85	13.849%	$54.4767	$54.48	$54.50	$54.50
Purchase #7	$106.63	4.661%	$111.6	$111.60	$111.60	$111.60
7 purchase totals =	$920.88		$989.6996	$989.69	$989.75	$989.70