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	$11.67	5.258%	$12.2836	$12.28	$12.30	$12.30
Purchase #2	$184.37	13.487%	$209.236	$209.24	$209.25	$209.20
Purchase #3	$136.25	3.431%	$140.9247	$140.92	$140.90	$140.90
Purchase #4	$227.34	6.210%	$241.4578	$241.46	$241.45	$241.50
Purchase #5	$60.69	10.489%	$67.0558	$67.06	$67.05	$67.10
Purchase #6	$38.63	13.705%	$43.9242	$43.92	$43.90	$43.90
Purchase #7	$152.88	13.302%	$173.2161	$173.22	$173.20	$173.20
7 purchase totals =	$811.83		$888.0982	$888.10	$888.05	$888.10