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	$29.49	5.365%	$31.0721	$31.07	$31.05	$31.10
Purchase #2	$155.86	13.260%	$176.527	$176.53	$176.55	$176.50
Purchase #3	$132.73	8.459%	$143.9576	$143.96	$143.95	$144.00
Purchase #4	$104.40	6.599%	$111.2894	$111.29	$111.30	$111.30
Purchase #5	$139.49	7.674%	$150.1945	$150.19	$150.20	$150.20
Purchase #6	$61.84	4.279%	$64.4861	$64.49	$64.50	$64.50
Purchase #7	$88.43	3.609%	$91.6214	$91.62	$91.60	$91.60
7 purchase totals =	$712.24		$769.1481	$769.15	$769.15	$769.20