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	$126.32	5.490%	$133.255	$133.26	$133.25	$133.30
Purchase #2	$110.93	12.698%	$125.0159	$125.02	$125.00	$125.00
Purchase #3	$82.54	10.234%	$90.9871	$90.99	$91.00	$91.00
Purchase #4	$164.60	4.842%	$172.5699	$172.57	$172.55	$172.60
Purchase #5	$121.98	5.637%	$128.856	$128.86	$128.85	$128.90
Purchase #6	$100.42	9.155%	$109.6135	$109.61	$109.60	$109.60
Purchase #7	$37.70	7.468%	$40.5154	$40.52	$40.50	$40.50
7 purchase totals =	$744.49		$800.8128	$800.83	$800.75	$800.90