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	$56.85	11.867%	$63.5964	$63.60	$63.60	$63.60
Purchase #2	$68.76	8.740%	$74.7696	$74.77	$74.75	$74.80
Purchase #3	$27.52	11.219%	$30.6075	$30.61	$30.60	$30.60
Purchase #4	$169.83	4.147%	$176.8729	$176.87	$176.85	$176.90
Purchase #5	$139.54	3.260%	$144.089	$144.09	$144.10	$144.10
Purchase #6	$147.29	3.604%	$152.5983	$152.60	$152.60	$152.60
Purchase #7	$167.85	10.516%	$185.5011	$185.50	$185.50	$185.50
7 purchase totals =	$777.64		$828.0348	$828.04	$828.00	$828.10