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	$106.51	3.212%	$109.9311	$109.93	$109.95	$109.90
Purchase #2	$85.40	12.389%	$95.9802	$95.98	$96.00	$96.00
Purchase #3	$91.31	9.340%	$99.8384	$99.84	$99.85	$99.80
Purchase #4	$83.84	12.248%	$94.1087	$94.11	$94.10	$94.10
Purchase #5	$157.31	8.378%	$170.4894	$170.49	$170.50	$170.50
Purchase #6	$134.28	10.835%	$148.8292	$148.83	$148.85	$148.80
Purchase #7	$163.52	10.608%	$180.8662	$180.87	$180.85	$180.90
7 purchase totals =	$822.17		$900.0432	$900.05	$900.10	$900.00