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	$45.41	11.185%	$50.4891	$50.49	$50.50	$50.50
Purchase #2	$99.76	6.179%	$105.9242	$105.92	$105.90	$105.90
Purchase #3	$87.41	6.413%	$93.0156	$93.02	$93.00	$93.00
Purchase #4	$22.65	13.177%	$25.6346	$25.63	$25.65	$25.60
Purchase #5	$81.66	13.391%	$92.5951	$92.60	$92.60	$92.60
Purchase #6	$100.83	13.452%	$114.3937	$114.39	$114.40	$114.40
Purchase #7	$174.28	7.600%	$187.5253	$187.53	$187.55	$187.50
7 purchase totals =	$612.00		$669.5776	$669.58	$669.60	$669.50