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	$21.33	11.681%	$23.8216	$23.82	$23.80	$23.80
Purchase #2	$157.58	9.562%	$172.6478	$172.65	$172.65	$172.60
Purchase #3	$240.67	5.337%	$253.5146	$253.51	$253.50	$253.50
Purchase #4	$75.36	4.140%	$78.4799	$78.48	$78.50	$78.50
Purchase #5	$230.62	12.853%	$260.2616	$260.26	$260.25	$260.30
Purchase #6	$85.87	3.869%	$89.1923	$89.19	$89.20	$89.20
Purchase #7	$78.72	9.741%	$86.3881	$86.39	$86.40	$86.40
7 purchase totals =	$890.15		$964.3059	$964.30	$964.30	$964.30