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	$38.53	13.476%	$43.7223	$43.72	$43.70	$43.70
Purchase #2	$233.49	7.476%	$250.9457	$250.95	$250.95	$250.90
Purchase #3	$134.67	7.521%	$144.7985	$144.80	$144.80	$144.80
Purchase #4	$238.59	4.159%	$248.513	$248.51	$248.50	$248.50
Purchase #5	$144.92	4.669%	$151.6863	$151.69	$151.70	$151.70
Purchase #6	$202.54	5.177%	$213.0255	$213.03	$213.05	$213.00
Purchase #7	$26.73	4.224%	$27.8591	$27.86	$27.85	$27.90
7 purchase totals =	$1,019.47		$1,080.5504	$1,080.56	$1,080.55	$1,080.50