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	$69.89	12.579%	$78.6815	$78.68	$78.70	$78.70
Purchase #2	$115.55	13.641%	$131.3122	$131.31	$131.30	$131.30
Purchase #3	$145.41	8.116%	$157.2115	$157.21	$157.20	$157.20
Purchase #4	$139.46	4.848%	$146.221	$146.22	$146.20	$146.20
Purchase #5	$123.25	7.479%	$132.4679	$132.47	$132.45	$132.50
Purchase #6	$33.37	11.861%	$37.328	$37.33	$37.35	$37.30
Purchase #7	$196.57	7.215%	$210.7525	$210.75	$210.75	$210.80
7 purchase totals =	$823.50		$893.9746	$893.97	$893.95	$894.00