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	$248.43	8.845%	$270.4036	$270.40	$270.40	$270.40
Purchase #2	$139.59	8.606%	$151.6031	$151.60	$151.60	$151.60
Purchase #3	$128.54	11.608%	$143.4609	$143.46	$143.45	$143.50
Purchase #4	$63.75	3.329%	$65.8722	$65.87	$65.85	$65.90
Purchase #5	$228.30	8.299%	$247.2466	$247.25	$247.25	$247.20
Purchase #6	$156.32	11.617%	$174.4797	$174.48	$174.50	$174.50
Purchase #7	$65.62	13.182%	$74.27	$74.27	$74.25	$74.30
7 purchase totals =	$1,030.55		$1,127.3361	$1,127.33	$1,127.30	$1,127.40