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	$56.28	12.534%	$63.3341	$63.33	$63.35	$63.30
Purchase #2	$242.57	3.842%	$251.8895	$251.89	$251.90	$251.90
Purchase #3	$56.88	9.528%	$62.2995	$62.30	$62.30	$62.30
Purchase #4	$176.48	5.630%	$186.4158	$186.42	$186.40	$186.40
Purchase #5	$95.88	3.564%	$99.2972	$99.30	$99.30	$99.30
Purchase #6	$96.85	12.556%	$109.0105	$109.01	$109.00	$109.00
Purchase #7	$139.95	8.470%	$151.8038	$151.80	$151.80	$151.80
7 purchase totals =	$864.89		$924.0504	$924.05	$924.05	$924.00