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	$231.72	7.286%	$248.6031	$248.60	$248.60	$248.60
Purchase #2	$89.32	9.595%	$97.8903	$97.89	$97.90	$97.90
Purchase #3	$115.72	3.649%	$119.9426	$119.94	$119.95	$119.90
Purchase #4	$120.36	8.749%	$130.8903	$130.89	$130.90	$130.90
Purchase #5	$228.58	8.390%	$247.7579	$247.76	$247.75	$247.80
Purchase #6	$99.79	4.662%	$104.4422	$104.44	$104.45	$104.40
Purchase #7	$86.67	3.272%	$89.5058	$89.51	$89.50	$89.50
7 purchase totals =	$972.16		$1,039.0322	$1,039.03	$1,039.05	$1,039.00