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	$205.30	11.799%	$229.5233	$229.52	$229.50	$229.50
Purchase #2	$192.90	4.158%	$200.9208	$200.92	$200.90	$200.90
Purchase #3	$160.29	12.600%	$180.4865	$180.49	$180.50	$180.50
Purchase #4	$87.55	13.376%	$99.2607	$99.26	$99.25	$99.30
Purchase #5	$37.40	10.692%	$41.3988	$41.40	$41.40	$41.40
Purchase #6	$68.30	11.125%	$75.8984	$75.90	$75.90	$75.90
Purchase #7	$192.67	4.109%	$200.5868	$200.59	$200.60	$200.60
7 purchase totals =	$944.41		$1,028.0753	$1,028.08	$1,028.05	$1,028.10