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	$65.89	8.487%	$71.4821	$71.48	$71.50	$71.50
Purchase #2	$96.81	9.429%	$105.9382	$105.94	$105.95	$105.90
Purchase #3	$33.86	3.145%	$34.9249	$34.92	$34.90	$34.90
Purchase #4	$92.36	10.761%	$102.2989	$102.30	$102.30	$102.30
Purchase #5	$200.90	3.834%	$208.6025	$208.60	$208.60	$208.60
Purchase #6	$160.38	11.556%	$178.9135	$178.91	$178.90	$178.90
Purchase #7	$86.58	10.700%	$95.8441	$95.84	$95.85	$95.80
7 purchase totals =	$736.78		$798.0042	$797.99	$798.00	$797.90