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	$89.72	10.532%	$99.1693	$99.17	$99.15	$99.20
Purchase #2	$50.32	4.554%	$52.6116	$52.61	$52.60	$52.60
Purchase #3	$220.38	9.175%	$240.5999	$240.60	$240.60	$240.60
Purchase #4	$228.33	12.351%	$256.531	$256.53	$256.55	$256.50
Purchase #5	$225.54	13.592%	$256.1954	$256.20	$256.20	$256.20
Purchase #6	$136.28	11.707%	$152.2343	$152.23	$152.25	$152.20
Purchase #7	$59.66	12.534%	$67.1378	$67.14	$67.15	$67.10
7 purchase totals =	$1,010.23		$1,124.4793	$1,124.48	$1,124.50	$1,124.40