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	$247.57	4.664%	$259.1167	$259.12	$259.10	$259.10
Purchase #2	$67.58	4.133%	$70.3731	$70.37	$70.35	$70.40
Purchase #3	$50.60	7.836%	$54.565	$54.57	$54.55	$54.60
Purchase #4	$17.97	12.631%	$20.2398	$20.24	$20.25	$20.20
Purchase #5	$206.53	12.142%	$231.6069	$231.61	$231.60	$231.60
Purchase #6	$216.39	6.217%	$229.843	$229.84	$229.85	$229.80
Purchase #7	$112.46	13.195%	$127.2991	$127.30	$127.30	$127.30
7 purchase totals =	$919.10		$993.0436	$993.05	$993.00	$993.00