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	$57.84	11.394%	$64.4303	$64.43	$64.45	$64.40
Purchase #2	$167.73	11.201%	$186.5174	$186.52	$186.50	$186.50
Purchase #3	$91.82	3.233%	$94.7885	$94.79	$94.80	$94.80
Purchase #4	$85.65	6.338%	$91.0785	$91.08	$91.10	$91.10
Purchase #5	$12.27	8.563%	$13.3207	$13.32	$13.30	$13.30
Purchase #6	$188.94	12.445%	$212.4536	$212.45	$212.45	$212.50
Purchase #7	$38.38	12.690%	$43.2504	$43.25	$43.25	$43.30
7 purchase totals =	$642.63		$705.8394	$705.84	$705.85	$705.90