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	$136.85	12.166%	$153.4992	$153.50	$153.50	$153.50
Purchase #2	$37.69	7.647%	$40.5722	$40.57	$40.55	$40.60
Purchase #3	$67.56	4.834%	$70.8259	$70.83	$70.85	$70.80
Purchase #4	$108.78	5.628%	$114.9021	$114.90	$114.90	$114.90
Purchase #5	$140.46	7.557%	$151.0746	$151.07	$151.05	$151.10
Purchase #6	$49.40	5.222%	$51.9797	$51.98	$52.00	$52.00
Purchase #7	$224.49	7.180%	$240.6084	$240.61	$240.60	$240.60
7 purchase totals =	$765.23		$823.4621	$823.46	$823.45	$823.50