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	$158.74	13.382%	$179.9826	$179.98	$180.00	$180.00
Purchase #2	$91.85	9.168%	$100.2708	$100.27	$100.25	$100.30
Purchase #3	$26.32	4.437%	$27.4878	$27.49	$27.50	$27.50
Purchase #4	$6.49	10.440%	$7.1676	$7.17	$7.15	$7.20
Purchase #5	$98.45	4.660%	$103.0378	$103.04	$103.05	$103.00
Purchase #6	$128.56	6.481%	$136.892	$136.89	$136.90	$136.90
Purchase #7	$220.97	6.228%	$234.732	$234.73	$234.75	$234.70
7 purchase totals =	$731.38		$789.5706	$789.57	$789.60	$789.60