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	$123.85	8.492%	$134.3673	$134.37	$134.35	$134.40
Purchase #2	$232.35	10.116%	$255.8545	$255.85	$255.85	$255.90
Purchase #3	$105.27	5.337%	$110.8883	$110.89	$110.90	$110.90
Purchase #4	$89.46	5.758%	$94.6111	$94.61	$94.60	$94.60
Purchase #5	$52.39	11.366%	$58.3446	$58.34	$58.35	$58.30
Purchase #6	$59.30	3.685%	$61.4852	$61.49	$61.50	$61.50
Purchase #7	$19.42	9.115%	$21.1901	$21.19	$21.20	$21.20
7 purchase totals =	$682.04		$736.7411	$736.74	$736.75	$736.80