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	$19.89	11.532%	$22.1837	$22.18	$22.20	$22.20
Purchase #2	$6.35	11.833%	$7.1014	$7.10	$7.10	$7.10
Purchase #3	$116.37	5.613%	$122.9018	$122.90	$122.90	$122.90
Purchase #4	$173.94	13.193%	$196.8879	$196.89	$196.90	$196.90
Purchase #5	$142.38	9.434%	$155.8121	$155.81	$155.80	$155.80
Purchase #6	$137.42	13.609%	$156.1215	$156.12	$156.10	$156.10
Purchase #7	$100.51	9.380%	$109.9378	$109.94	$109.95	$109.90
7 purchase totals =	$696.86		$770.9462	$770.94	$770.95	$770.90