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	$94.51	6.615%	$100.7618	$100.76	$100.75	$100.80
Purchase #2	$153.99	6.773%	$164.4197	$164.42	$164.40	$164.40
Purchase #3	$216.50	8.608%	$235.1363	$235.14	$235.15	$235.10
Purchase #4	$155.89	8.280%	$168.7977	$168.80	$168.80	$168.80
Purchase #5	$39.69	6.185%	$42.1448	$42.14	$42.15	$42.10
Purchase #6	$91.81	4.424%	$95.8717	$95.87	$95.85	$95.90
Purchase #7	$76.50	9.674%	$83.9006	$83.90	$83.90	$83.90
7 purchase totals =	$828.89		$891.0326	$891.03	$891.00	$891.00