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	$209.56	13.647%	$238.1587	$238.16	$238.15	$238.20
Purchase #2	$98.40	7.732%	$106.0083	$106.01	$106.00	$106.00
Purchase #3	$240.48	3.819%	$249.6639	$249.66	$249.65	$249.70
Purchase #4	$16.50	12.789%	$18.6102	$18.61	$18.60	$18.60
Purchase #5	$208.87	6.328%	$222.0873	$222.09	$222.10	$222.10
Purchase #6	$104.83	4.128%	$109.1574	$109.16	$109.15	$109.20
Purchase #7	$34.60	10.273%	$38.1545	$38.15	$38.15	$38.20
7 purchase totals =	$913.24		$981.8403	$981.84	$981.80	$982.00