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	$19.53	5.123%	$20.5305	$20.53	$20.55	$20.50
Purchase #2	$231.41	9.460%	$253.3014	$253.30	$253.30	$253.30
Purchase #3	$246.50	6.390%	$262.2514	$262.25	$262.25	$262.30
Purchase #4	$95.27	4.199%	$99.2704	$99.27	$99.25	$99.30
Purchase #5	$124.35	6.475%	$132.4017	$132.40	$132.40	$132.40
Purchase #6	$60.53	13.646%	$68.7899	$68.79	$68.80	$68.80
Purchase #7	$140.37	4.639%	$146.8818	$146.88	$146.90	$146.90
7 purchase totals =	$917.96		$983.4271	$983.42	$983.45	$983.50