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	$123.53	13.123%	$139.7408	$139.74	$139.75	$139.70
Purchase #2	$86.46	13.713%	$98.3163	$98.32	$98.30	$98.30
Purchase #3	$122.60	13.505%	$139.1571	$139.16	$139.15	$139.20
Purchase #4	$23.69	9.171%	$25.8626	$25.86	$25.85	$25.90
Purchase #5	$101.92	3.638%	$105.6278	$105.63	$105.65	$105.60
Purchase #6	$176.78	3.594%	$183.1335	$183.13	$183.15	$183.10
Purchase #7	$43.51	4.131%	$45.3074	$45.31	$45.30	$45.30
7 purchase totals =	$678.49		$737.1455	$737.15	$737.15	$737.10