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	$25.70	11.263%	$28.5946	$28.59	$28.60	$28.60
Purchase #2	$202.69	5.201%	$213.2319	$213.23	$213.25	$213.20
Purchase #3	$67.64	11.547%	$75.4504	$75.45	$75.45	$75.50
Purchase #4	$238.47	10.485%	$263.4736	$263.47	$263.45	$263.50
Purchase #5	$133.51	8.508%	$144.869	$144.87	$144.85	$144.90
Purchase #6	$87.75	3.610%	$90.9178	$90.92	$90.90	$90.90
Purchase #7	$132.36	10.665%	$146.4762	$146.48	$146.50	$146.50
7 purchase totals =	$888.12		$963.0135	$963.01	$963.00	$963.10