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	$80.50	11.701%	$89.9193	$89.92	$89.90	$89.90
Purchase #2	$188.85	12.696%	$212.8264	$212.83	$212.85	$212.80
Purchase #3	$34.49	11.722%	$38.5329	$38.53	$38.55	$38.50
Purchase #4	$167.39	3.633%	$173.4713	$173.47	$173.45	$173.50
Purchase #5	$94.77	4.546%	$99.0782	$99.08	$99.10	$99.10
Purchase #6	$95.79	10.805%	$106.1401	$106.14	$106.15	$106.10
Purchase #7	$88.93	8.642%	$96.6153	$96.62	$96.60	$96.60
7 purchase totals =	$750.72		$816.5835	$816.59	$816.60	$816.50