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	$138.78	6.736%	$148.1282	$148.13	$148.15	$148.10
Purchase #2	$212.31	7.795%	$228.8596	$228.86	$228.85	$228.90
Purchase #3	$52.45	12.408%	$58.958	$58.96	$58.95	$59.00
Purchase #4	$61.55	12.820%	$69.4407	$69.44	$69.45	$69.40
Purchase #5	$92.80	7.868%	$100.1015	$100.10	$100.10	$100.10
Purchase #6	$231.54	3.195%	$238.9377	$238.94	$238.95	$238.90
Purchase #7	$150.57	9.136%	$164.3261	$164.33	$164.35	$164.30
7 purchase totals =	$940.00		$1,008.7518	$1,008.76	$1,008.80	$1,008.70