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	$71.81	9.756%	$78.8158	$78.82	$78.80	$78.80
Purchase #2	$249.42	8.262%	$270.0271	$270.03	$270.05	$270.00
Purchase #3	$238.33	6.501%	$253.8238	$253.82	$253.80	$253.80
Purchase #4	$138.69	3.466%	$143.497	$143.50	$143.50	$143.50
Purchase #5	$68.55	10.550%	$75.782	$75.78	$75.80	$75.80
Purchase #6	$71.48	5.293%	$75.2634	$75.26	$75.25	$75.30
Purchase #7	$243.31	4.221%	$253.5801	$253.58	$253.60	$253.60
7 purchase totals =	$1,081.59		$1,150.7892	$1,150.79	$1,150.80	$1,150.80