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	$91.60	8.448%	$99.3384	$99.34	$99.35	$99.30
Purchase #2	$128.27	12.271%	$144.01	$144.01	$144.00	$144.00
Purchase #3	$78.93	6.231%	$83.8481	$83.85	$83.85	$83.80
Purchase #4	$146.43	3.333%	$151.3105	$151.31	$151.30	$151.30
Purchase #5	$12.47	3.125%	$12.8597	$12.86	$12.85	$12.90
Purchase #6	$60.71	7.297%	$65.14	$65.14	$65.15	$65.10
Purchase #7	$25.97	8.544%	$28.1889	$28.19	$28.20	$28.20
7 purchase totals =	$544.38		$584.6956	$584.70	$584.70	$584.60