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	$41.39	10.576%	$45.7674	$45.77	$45.75	$45.80
Purchase #2	$179.33	8.349%	$194.3023	$194.30	$194.30	$194.30
Purchase #3	$135.73	11.300%	$151.0675	$151.07	$151.05	$151.10
Purchase #4	$29.62	7.566%	$31.861	$31.86	$31.85	$31.90
Purchase #5	$49.88	3.238%	$51.4951	$51.50	$51.50	$51.50
Purchase #6	$90.66	10.689%	$100.3506	$100.35	$100.35	$100.40
Purchase #7	$51.84	8.801%	$56.4024	$56.40	$56.40	$56.40
7 purchase totals =	$578.45		$631.2463	$631.25	$631.20	$631.40