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	$250.26	11.296%	$278.5294	$278.53	$278.55	$278.50
Purchase #2	$93.55	6.315%	$99.4577	$99.46	$99.45	$99.50
Purchase #3	$52.42	8.508%	$56.8799	$56.88	$56.90	$56.90
Purchase #4	$18.38	7.853%	$19.8234	$19.82	$19.80	$19.80
Purchase #5	$8.28	12.204%	$9.2905	$9.29	$9.30	$9.30
Purchase #6	$64.67	4.606%	$67.6487	$67.65	$67.65	$67.60
Purchase #7	$118.97	7.490%	$127.8809	$127.88	$127.90	$127.90
7 purchase totals =	$606.53		$659.5105	$659.51	$659.55	$659.50