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	$81.52	10.667%	$90.2157	$90.22	$90.20	$90.20
Purchase #2	$19.36	7.219%	$20.7576	$20.76	$20.75	$20.80
Purchase #3	$164.70	8.755%	$179.1195	$179.12	$179.10	$179.10
Purchase #4	$56.78	7.471%	$61.022	$61.02	$61.00	$61.00
Purchase #5	$20.85	7.176%	$22.3462	$22.35	$22.35	$22.30
Purchase #6	$37.31	10.359%	$41.1749	$41.17	$41.15	$41.20
Purchase #7	$23.31	8.726%	$25.344	$25.34	$25.35	$25.30
7 purchase totals =	$403.83		$439.9799	$439.98	$439.90	$439.90