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	$229.82	11.311%	$255.8149	$255.81	$255.80	$255.80
Purchase #2	$40.67	7.467%	$43.7068	$43.71	$43.70	$43.70
Purchase #3	$44.57	10.382%	$49.1973	$49.20	$49.20	$49.20
Purchase #4	$120.55	3.284%	$124.5089	$124.51	$124.50	$124.50
Purchase #5	$143.54	4.692%	$150.2749	$150.27	$150.25	$150.30
Purchase #6	$85.66	6.505%	$91.2322	$91.23	$91.25	$91.20
Purchase #7	$148.38	12.665%	$167.1723	$167.17	$167.15	$167.20
7 purchase totals =	$813.19		$881.9073	$881.90	$881.85	$881.90