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	$34.58	5.522%	$36.4895	$36.49	$36.50	$36.50
Purchase #2	$101.39	9.810%	$111.3364	$111.34	$111.35	$111.30
Purchase #3	$220.41	11.219%	$245.1378	$245.14	$245.15	$245.10
Purchase #4	$159.87	3.483%	$165.4383	$165.44	$165.45	$165.40
Purchase #5	$147.32	9.626%	$161.501	$161.50	$161.50	$161.50
Purchase #6	$237.43	13.806%	$270.2096	$270.21	$270.20	$270.20
Purchase #7	$142.73	6.840%	$152.4927	$152.49	$152.50	$152.50
7 purchase totals =	$1,043.73		$1,142.6053	$1,142.61	$1,142.65	$1,142.50