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	$43.34	5.695%	$45.8082	$45.81	$45.80	$45.80
Purchase #2	$113.43	13.218%	$128.4232	$128.42	$128.40	$128.40
Purchase #3	$174.78	6.402%	$185.9694	$185.97	$185.95	$186.00
Purchase #4	$93.51	7.817%	$100.8197	$100.82	$100.80	$100.80
Purchase #5	$65.93	9.444%	$72.1564	$72.16	$72.15	$72.20
Purchase #6	$86.28	10.794%	$95.5931	$95.59	$95.60	$95.60
Purchase #7	$68.83	10.257%	$75.8899	$75.89	$75.90	$75.90
7 purchase totals =	$646.10		$704.6599	$704.66	$704.60	$704.70