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	$143.83	3.542%	$148.9245	$148.92	$148.90	$148.90
Purchase #2	$181.88	4.673%	$190.3793	$190.38	$190.40	$190.40
Purchase #3	$92.73	8.626%	$100.7289	$100.73	$100.75	$100.70
Purchase #4	$87.30	4.644%	$91.3542	$91.35	$91.35	$91.40
Purchase #5	$64.42	12.503%	$72.4744	$72.47	$72.45	$72.50
Purchase #6	$205.42	5.375%	$216.4613	$216.46	$216.45	$216.50
Purchase #7	$19.36	7.316%	$20.7764	$20.78	$20.80	$20.80
7 purchase totals =	$794.94		$841.0990	$841.09	$841.10	$841.20