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	$85.50	5.541%	$90.2376	$90.24	$90.25	$90.20
Purchase #2	$235.99	13.271%	$267.3082	$267.31	$267.30	$267.30
Purchase #3	$139.40	11.715%	$155.7307	$155.73	$155.75	$155.70
Purchase #4	$50.27	9.193%	$54.8913	$54.89	$54.90	$54.90
Purchase #5	$100.66	10.711%	$111.4417	$111.44	$111.45	$111.40
Purchase #6	$110.42	6.281%	$117.3555	$117.36	$117.35	$117.40
Purchase #7	$152.90	12.845%	$172.54	$172.54	$172.55	$172.50
7 purchase totals =	$875.14		$969.5050	$969.51	$969.55	$969.40