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	$83.30	8.357%	$90.2614	$90.26	$90.25	$90.30
Purchase #2	$88.45	4.554%	$92.478	$92.48	$92.50	$92.50
Purchase #3	$187.89	12.228%	$210.8652	$210.87	$210.85	$210.90
Purchase #4	$231.29	7.839%	$249.4208	$249.42	$249.40	$249.40
Purchase #5	$89.73	7.390%	$96.361	$96.36	$96.35	$96.40
Purchase #6	$132.45	10.618%	$146.5135	$146.51	$146.50	$146.50
Purchase #7	$9.51	7.631%	$10.2357	$10.24	$10.25	$10.20
7 purchase totals =	$822.62		$896.1356	$896.14	$896.10	$896.20