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	$250.99	8.341%	$271.9251	$271.93	$271.95	$271.90
Purchase #2	$248.29	10.267%	$273.7819	$273.78	$273.80	$273.80
Purchase #3	$182.73	6.262%	$194.1726	$194.17	$194.15	$194.20
Purchase #4	$89.53	5.808%	$94.7299	$94.73	$94.75	$94.70
Purchase #5	$105.44	3.763%	$109.4077	$109.41	$109.40	$109.40
Purchase #6	$19.53	6.420%	$20.7838	$20.78	$20.80	$20.80
Purchase #7	$92.93	4.209%	$96.8414	$96.84	$96.85	$96.80
7 purchase totals =	$989.44		$1,061.6424	$1,061.64	$1,061.70	$1,061.60