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	$113.75	13.217%	$128.7843	$128.78	$128.80	$128.80
Purchase #2	$85.61	11.606%	$95.5459	$95.55	$95.55	$95.50
Purchase #3	$108.40	6.248%	$115.1728	$115.17	$115.15	$115.20
Purchase #4	$86.77	6.106%	$92.0682	$92.07	$92.05	$92.10
Purchase #5	$120.50	3.328%	$124.5102	$124.51	$124.50	$124.50
Purchase #6	$35.88	4.440%	$37.4731	$37.47	$37.45	$37.50
Purchase #7	$41.55	13.179%	$47.0259	$47.03	$47.05	$47.00
7 purchase totals =	$592.46		$640.5804	$640.58	$640.55	$640.60