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	$28.46	13.551%	$32.3166	$32.32	$32.30	$32.30
Purchase #2	$100.75	3.394%	$104.1695	$104.17	$104.15	$104.20
Purchase #3	$75.43	9.366%	$82.4948	$82.49	$82.50	$82.50
Purchase #4	$197.35	12.803%	$222.6167	$222.62	$222.60	$222.60
Purchase #5	$220.65	8.459%	$239.3148	$239.31	$239.30	$239.30
Purchase #6	$139.34	9.291%	$152.2861	$152.29	$152.30	$152.30
Purchase #7	$49.38	13.774%	$56.1816	$56.18	$56.20	$56.20
7 purchase totals =	$811.36		$889.3801	$889.38	$889.35	$889.40