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	$86.82	13.455%	$98.5016	$98.50	$98.50	$98.50
Purchase #2	$232.31	11.600%	$259.258	$259.26	$259.25	$259.30
Purchase #3	$134.25	7.362%	$144.1335	$144.13	$144.15	$144.10
Purchase #4	$224.72	6.523%	$239.3785	$239.38	$239.40	$239.40
Purchase #5	$64.93	5.674%	$68.6141	$68.61	$68.60	$68.60
Purchase #6	$82.43	3.303%	$85.1527	$85.15	$85.15	$85.20
Purchase #7	$13.87	11.786%	$15.5047	$15.50	$15.50	$15.50
7 purchase totals =	$839.33		$910.5431	$910.53	$910.55	$910.60