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	$234.37	6.692%	$250.054	$250.05	$250.05	$250.10
Purchase #2	$95.58	8.406%	$103.6145	$103.61	$103.60	$103.60
Purchase #3	$95.85	4.834%	$100.4834	$100.48	$100.50	$100.50
Purchase #4	$85.28	12.255%	$95.7311	$95.73	$95.75	$95.70
Purchase #5	$72.96	7.606%	$78.5093	$78.51	$78.50	$78.50
Purchase #6	$59.97	10.119%	$66.0384	$66.04	$66.05	$66.00
Purchase #7	$171.39	8.810%	$186.4895	$186.49	$186.50	$186.50
7 purchase totals =	$815.40		$880.9202	$880.91	$880.95	$880.90