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	$24.90	12.479%	$28.0073	$28.01	$28.00	$28.00
Purchase #2	$19.61	13.452%	$22.2479	$22.25	$22.25	$22.20
Purchase #3	$91.65	8.383%	$99.333	$99.33	$99.35	$99.30
Purchase #4	$166.99	12.323%	$187.5682	$187.57	$187.55	$187.60
Purchase #5	$54.51	8.805%	$59.3096	$59.31	$59.30	$59.30
Purchase #6	$161.75	4.107%	$168.3931	$168.39	$168.40	$168.40
Purchase #7	$49.42	6.431%	$52.5982	$52.60	$52.60	$52.60
7 purchase totals =	$568.83		$617.4573	$617.46	$617.45	$617.40