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	$129.98	3.748%	$134.8517	$134.85	$134.85	$134.90
Purchase #2	$89.56	6.402%	$95.2936	$95.29	$95.30	$95.30
Purchase #3	$216.91	3.488%	$224.4758	$224.48	$224.50	$224.50
Purchase #4	$12.92	10.757%	$14.3098	$14.31	$14.30	$14.30
Purchase #5	$107.52	10.538%	$118.8505	$118.85	$118.85	$118.90
Purchase #6	$18.27	12.606%	$20.5731	$20.57	$20.55	$20.60
Purchase #7	$234.71	5.569%	$247.781	$247.78	$247.80	$247.80
7 purchase totals =	$809.87		$856.1355	$856.13	$856.15	$856.30