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	$183.28	5.239%	$192.882	$192.88	$192.90	$192.90
Purchase #2	$243.82	6.171%	$258.8661	$258.87	$258.85	$258.90
Purchase #3	$31.94	11.432%	$35.5914	$35.59	$35.60	$35.60
Purchase #4	$59.57	12.181%	$66.8262	$66.83	$66.85	$66.80
Purchase #5	$101.43	3.826%	$105.3107	$105.31	$105.30	$105.30
Purchase #6	$127.82	8.646%	$138.8713	$138.87	$138.85	$138.90
Purchase #7	$95.83	6.687%	$102.2382	$102.24	$102.25	$102.20
7 purchase totals =	$843.69		$900.5859	$900.59	$900.60	$900.60