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	$153.69	4.458%	$160.5415	$160.54	$160.55	$160.50
Purchase #2	$206.59	13.337%	$234.1429	$234.14	$234.15	$234.10
Purchase #3	$167.26	5.175%	$175.9157	$175.92	$175.90	$175.90
Purchase #4	$73.34	8.239%	$79.3825	$79.38	$79.40	$79.40
Purchase #5	$250.49	12.820%	$282.6028	$282.60	$282.60	$282.60
Purchase #6	$91.38	10.333%	$100.8223	$100.82	$100.80	$100.80
Purchase #7	$168.84	12.843%	$190.5241	$190.52	$190.50	$190.50
7 purchase totals =	$1,111.59		$1,223.9318	$1,223.92	$1,223.90	$1,223.80