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	$86.48	4.649%	$90.5005	$90.50	$90.50	$90.50
Purchase #2	$101.35	11.196%	$112.6971	$112.70	$112.70	$112.70
Purchase #3	$80.79	5.340%	$85.1042	$85.10	$85.10	$85.10
Purchase #4	$203.96	11.182%	$226.7668	$226.77	$226.75	$226.80
Purchase #5	$173.97	13.394%	$197.2715	$197.27	$197.25	$197.30
Purchase #6	$40.57	4.751%	$42.4975	$42.50	$42.50	$42.50
Purchase #7	$59.94	9.832%	$65.8333	$65.83	$65.85	$65.80
7 purchase totals =	$747.06		$820.6709	$820.67	$820.65	$820.70