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	$72.40	10.274%	$79.8384	$79.84	$79.85	$79.80
Purchase #2	$125.37	13.757%	$142.6172	$142.62	$142.60	$142.60
Purchase #3	$182.30	10.154%	$200.8107	$200.81	$200.80	$200.80
Purchase #4	$138.98	4.849%	$145.7191	$145.72	$145.70	$145.70
Purchase #5	$95.66	3.351%	$98.8656	$98.87	$98.85	$98.90
Purchase #6	$98.33	7.108%	$105.3193	$105.32	$105.30	$105.30
Purchase #7	$139.50	5.720%	$147.4794	$147.48	$147.50	$147.50
7 purchase totals =	$852.54		$920.6497	$920.66	$920.60	$920.60