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	$41.64	8.304%	$45.0978	$45.10	$45.10	$45.10
Purchase #2	$92.43	7.778%	$99.6192	$99.62	$99.60	$99.60
Purchase #3	$35.57	5.332%	$37.4666	$37.47	$37.45	$37.50
Purchase #4	$153.83	5.165%	$161.7753	$161.78	$161.80	$161.80
Purchase #5	$55.31	7.172%	$59.2768	$59.28	$59.30	$59.30
Purchase #6	$167.59	10.310%	$184.8685	$184.87	$184.85	$184.90
Purchase #7	$45.56	8.598%	$49.4772	$49.48	$49.50	$49.50
7 purchase totals =	$591.93		$637.5814	$637.60	$637.60	$637.70