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	$90.81	9.191%	$99.1563	$99.16	$99.15	$99.20
Purchase #2	$38.52	7.314%	$41.3374	$41.34	$41.35	$41.30
Purchase #3	$227.48	10.343%	$251.0083	$251.01	$251.00	$251.00
Purchase #4	$238.95	6.321%	$254.054	$254.05	$254.05	$254.10
Purchase #5	$211.51	6.296%	$224.8267	$224.83	$224.85	$224.80
Purchase #6	$167.54	13.798%	$190.6572	$190.66	$190.65	$190.70
Purchase #7	$219.52	10.210%	$241.933	$241.93	$241.95	$241.90
7 purchase totals =	$1,194.33		$1,302.9729	$1,302.98	$1,303.00	$1,303.00