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	$6.90	6.648%	$7.3587	$7.36	$7.35	$7.40
Purchase #2	$195.71	6.704%	$208.8304	$208.83	$208.85	$208.80
Purchase #3	$217.90	7.245%	$233.6869	$233.69	$233.70	$233.70
Purchase #4	$247.28	4.170%	$257.5916	$257.59	$257.60	$257.60
Purchase #5	$150.80	6.776%	$161.0182	$161.02	$161.00	$161.00
Purchase #6	$40.29	12.666%	$45.3931	$45.39	$45.40	$45.40
Purchase #7	$57.51	11.562%	$64.1593	$64.16	$64.15	$64.20
7 purchase totals =	$916.39		$978.0382	$978.04	$978.05	$978.10