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	$222.99	12.648%	$251.1938	$251.19	$251.20	$251.20
Purchase #2	$117.50	8.869%	$127.9211	$127.92	$127.90	$127.90
Purchase #3	$181.92	3.859%	$188.9403	$188.94	$188.95	$188.90
Purchase #4	$120.87	12.676%	$136.1915	$136.19	$136.20	$136.20
Purchase #5	$62.28	6.682%	$66.4415	$66.44	$66.45	$66.40
Purchase #6	$42.34	6.831%	$45.2322	$45.23	$45.25	$45.20
Purchase #7	$11.99	13.443%	$13.6018	$13.60	$13.60	$13.60
7 purchase totals =	$759.89		$829.5222	$829.51	$829.55	$829.40