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	$37.81	8.176%	$40.9013	$40.90	$40.90	$40.90
Purchase #2	$55.49	7.233%	$59.5036	$59.50	$59.50	$59.50
Purchase #3	$200.53	10.475%	$221.5355	$221.54	$221.55	$221.50
Purchase #4	$245.91	12.282%	$276.1127	$276.11	$276.10	$276.10
Purchase #5	$26.62	6.827%	$28.4373	$28.44	$28.45	$28.40
Purchase #6	$100.78	13.440%	$114.3248	$114.32	$114.30	$114.30
Purchase #7	$146.66	4.336%	$153.0192	$153.02	$153.00	$153.00
7 purchase totals =	$813.80		$893.8344	$893.83	$893.80	$893.70