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	$86.52	4.117%	$90.082	$90.08	$90.10	$90.10
Purchase #2	$140.54	3.470%	$145.4167	$145.42	$145.40	$145.40
Purchase #3	$23.37	9.410%	$25.5691	$25.57	$25.55	$25.60
Purchase #4	$162.75	6.670%	$173.6054	$173.61	$173.60	$173.60
Purchase #5	$24.90	8.463%	$27.0073	$27.01	$27.00	$27.00
Purchase #6	$38.84	6.165%	$41.2345	$41.23	$41.25	$41.20
Purchase #7	$95.41	5.770%	$100.9152	$100.92	$100.90	$100.90
7 purchase totals =	$572.33		$603.8302	$603.84	$603.80	$603.80