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	$17.45	5.276%	$18.3707	$18.37	$18.35	$18.40
Purchase #2	$223.77	6.483%	$238.277	$238.28	$238.30	$238.30
Purchase #3	$42.63	4.830%	$44.689	$44.69	$44.70	$44.70
Purchase #4	$38.72	5.805%	$40.9677	$40.97	$40.95	$41.00
Purchase #5	$156.59	12.682%	$176.4487	$176.45	$176.45	$176.40
Purchase #6	$141.83	9.874%	$155.8343	$155.83	$155.85	$155.80
Purchase #7	$135.32	4.429%	$141.3133	$141.31	$141.30	$141.30
7 purchase totals =	$756.31		$815.9007	$815.90	$815.90	$815.90