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	$12.53	5.687%	$13.2426	$13.24	$13.25	$13.20
Purchase #2	$86.46	13.408%	$98.0526	$98.05	$98.05	$98.10
Purchase #3	$155.48	4.506%	$162.4859	$162.49	$162.50	$162.50
Purchase #4	$115.37	4.797%	$120.9043	$120.90	$120.90	$120.90
Purchase #5	$146.89	3.136%	$151.4965	$151.50	$151.50	$151.50
Purchase #6	$141.67	11.127%	$157.4336	$157.43	$157.45	$157.40
Purchase #7	$95.30	5.237%	$100.2909	$100.29	$100.30	$100.30
7 purchase totals =	$753.70		$803.9064	$803.90	$803.95	$803.90