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	$129.42	4.151%	$134.7922	$134.79	$134.80	$134.80
Purchase #2	$40.89	12.216%	$45.8851	$45.89	$45.90	$45.90
Purchase #3	$134.30	7.130%	$143.8756	$143.88	$143.90	$143.90
Purchase #4	$170.95	8.144%	$184.8722	$184.87	$184.85	$184.90
Purchase #5	$229.28	7.674%	$246.8749	$246.87	$246.85	$246.90
Purchase #6	$180.40	4.485%	$188.4909	$188.49	$188.50	$188.50
Purchase #7	$19.78	5.756%	$20.9185	$20.92	$20.90	$20.90
7 purchase totals =	$905.02		$965.7094	$965.71	$965.70	$965.80