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	$128.83	13.710%	$146.4926	$146.49	$146.50	$146.50
Purchase #2	$16.70	11.761%	$18.6641	$18.66	$18.65	$18.70
Purchase #3	$99.68	12.266%	$111.9067	$111.91	$111.90	$111.90
Purchase #4	$215.64	5.483%	$227.4635	$227.46	$227.45	$227.50
Purchase #5	$80.48	10.393%	$88.8443	$88.84	$88.85	$88.80
Purchase #6	$71.67	6.370%	$76.2354	$76.24	$76.25	$76.20
Purchase #7	$17.55	13.544%	$19.927	$19.93	$19.95	$19.90
7 purchase totals =	$630.55		$689.5336	$689.53	$689.55	$689.50