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	$103.89	6.366%	$110.5036	$110.50	$110.50	$110.50
Purchase #2	$88.73	13.510%	$100.7174	$100.72	$100.70	$100.70
Purchase #3	$93.31	10.762%	$103.352	$103.35	$103.35	$103.40
Purchase #4	$79.34	4.433%	$82.8571	$82.86	$82.85	$82.90
Purchase #5	$208.78	9.742%	$229.1193	$229.12	$229.10	$229.10
Purchase #6	$97.35	5.731%	$102.9291	$102.93	$102.95	$102.90
Purchase #7	$205.43	10.460%	$226.918	$226.92	$226.90	$226.90
7 purchase totals =	$876.83		$956.3965	$956.40	$956.35	$956.40