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	$89.96	10.402%	$99.3176	$99.32	$99.30	$99.30
Purchase #2	$23.52	5.821%	$24.8891	$24.89	$24.90	$24.90
Purchase #3	$227.97	10.277%	$251.3985	$251.40	$251.40	$251.40
Purchase #4	$115.66	9.699%	$126.8779	$126.88	$126.90	$126.90
Purchase #5	$44.64	5.106%	$46.9193	$46.92	$46.90	$46.90
Purchase #6	$223.62	7.600%	$240.6151	$240.62	$240.60	$240.60
Purchase #7	$40.87	5.865%	$43.267	$43.27	$43.25	$43.30
7 purchase totals =	$766.24		$833.2845	$833.30	$833.25	$833.30