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	$90.39	11.458%	$100.7469	$100.75	$100.75	$100.70
Purchase #2	$90.33	10.245%	$99.5843	$99.58	$99.60	$99.60
Purchase #3	$48.90	4.373%	$51.0384	$51.04	$51.05	$51.00
Purchase #4	$29.49	10.761%	$32.6634	$32.66	$32.65	$32.70
Purchase #5	$19.84	5.711%	$20.9731	$20.97	$20.95	$21.00
Purchase #6	$230.51	4.719%	$241.3878	$241.39	$241.40	$241.40
Purchase #7	$26.90	4.565%	$28.128	$28.13	$28.15	$28.10
7 purchase totals =	$536.36		$574.5219	$574.52	$574.55	$574.50