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	$104.41	13.274%	$118.2694	$118.27	$118.25	$118.30
Purchase #2	$37.60	7.579%	$40.4497	$40.45	$40.45	$40.40
Purchase #3	$147.43	3.281%	$152.2672	$152.27	$152.25	$152.30
Purchase #4	$237.56	12.422%	$267.0697	$267.07	$267.05	$267.10
Purchase #5	$23.37	6.220%	$24.8236	$24.82	$24.80	$24.80
Purchase #6	$136.97	9.504%	$149.9876	$149.99	$150.00	$150.00
Purchase #7	$78.68	13.130%	$89.0107	$89.01	$89.00	$89.00
7 purchase totals =	$766.02		$841.8779	$841.88	$841.80	$841.90