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	$87.83	13.739%	$99.897	$99.90	$99.90	$99.90
Purchase #2	$148.75	13.149%	$168.3091	$168.31	$168.30	$168.30
Purchase #3	$207.52	5.321%	$218.5621	$218.56	$218.55	$218.60
Purchase #4	$104.39	8.803%	$113.5795	$113.58	$113.60	$113.60
Purchase #5	$108.88	4.238%	$113.4943	$113.49	$113.50	$113.50
Purchase #6	$10.79	4.331%	$11.2573	$11.26	$11.25	$11.30
Purchase #7	$62.36	7.212%	$66.8574	$66.86	$66.85	$66.90
7 purchase totals =	$730.52		$791.9567	$791.96	$791.95	$792.10