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	$127.46	8.210%	$137.9245	$137.92	$137.90	$137.90
Purchase #2	$113.65	11.443%	$126.655	$126.66	$126.65	$126.70
Purchase #3	$142.68	11.589%	$159.2152	$159.22	$159.20	$159.20
Purchase #4	$168.93	7.518%	$181.6302	$181.63	$181.65	$181.60
Purchase #5	$123.90	10.846%	$137.3382	$137.34	$137.35	$137.30
Purchase #6	$180.59	13.171%	$204.3755	$204.38	$204.40	$204.40
Purchase #7	$19.97	9.663%	$21.8997	$21.90	$21.90	$21.90
7 purchase totals =	$877.18		$969.0383	$969.05	$969.05	$969.00