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	$14.98	10.755%	$16.5911	$16.59	$16.60	$16.60
Purchase #2	$58.69	3.811%	$60.9267	$60.93	$60.95	$60.90
Purchase #3	$211.51	5.302%	$222.7243	$222.72	$222.70	$222.70
Purchase #4	$163.66	7.419%	$175.8019	$175.80	$175.80	$175.80
Purchase #5	$147.92	12.615%	$166.5801	$166.58	$166.60	$166.60
Purchase #6	$183.43	7.133%	$196.5141	$196.51	$196.50	$196.50
Purchase #7	$119.61	10.281%	$131.9071	$131.91	$131.90	$131.90
7 purchase totals =	$899.80		$971.0453	$971.04	$971.05	$971.00