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	$38.89	3.277%	$40.1644	$40.16	$40.15	$40.20
Purchase #2	$59.26	8.752%	$64.4464	$64.45	$64.45	$64.40
Purchase #3	$100.48	11.789%	$112.3256	$112.33	$112.35	$112.30
Purchase #4	$86.52	9.668%	$94.8848	$94.88	$94.90	$94.90
Purchase #5	$187.55	4.698%	$196.3611	$196.36	$196.35	$196.40
Purchase #6	$54.96	12.754%	$61.9696	$61.97	$61.95	$62.00
Purchase #7	$32.25	7.472%	$34.6597	$34.66	$34.65	$34.70
7 purchase totals =	$559.91		$604.8116	$604.81	$604.80	$604.90