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	$124.31	5.682%	$131.3733	$131.37	$131.35	$131.40
Purchase #2	$61.29	9.564%	$67.1518	$67.15	$67.15	$67.20
Purchase #3	$117.61	9.309%	$128.5583	$128.56	$128.55	$128.60
Purchase #4	$177.51	11.166%	$197.3308	$197.33	$197.35	$197.30
Purchase #5	$79.64	13.854%	$90.6733	$90.67	$90.65	$90.70
Purchase #6	$97.39	3.352%	$100.6545	$100.65	$100.65	$100.70
Purchase #7	$138.58	3.665%	$143.659	$143.66	$143.65	$143.70
7 purchase totals =	$796.33		$859.4010	$859.39	$859.35	$859.60