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	$173.41	3.741%	$179.8973	$179.90	$179.90	$179.90
Purchase #2	$18.50	7.198%	$19.8316	$19.83	$19.85	$19.80
Purchase #3	$197.25	8.717%	$214.4443	$214.44	$214.45	$214.40
Purchase #4	$106.40	3.230%	$109.8367	$109.84	$109.85	$109.80
Purchase #5	$121.41	12.852%	$137.0136	$137.01	$137.00	$137.00
Purchase #6	$147.35	6.443%	$156.8438	$156.84	$156.85	$156.80
Purchase #7	$150.44	6.743%	$160.5842	$160.58	$160.60	$160.60
7 purchase totals =	$914.76		$978.4515	$978.44	$978.50	$978.30