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	$48.73	3.789%	$50.5764	$50.58	$50.60	$50.60
Purchase #2	$174.49	6.243%	$185.3834	$185.38	$185.40	$185.40
Purchase #3	$153.87	9.476%	$168.4507	$168.45	$168.45	$168.50
Purchase #4	$95.81	7.493%	$102.989	$102.99	$103.00	$103.00
Purchase #5	$7.33	10.653%	$8.1109	$8.11	$8.10	$8.10
Purchase #6	$31.81	6.607%	$33.9117	$33.91	$33.90	$33.90
Purchase #7	$113.45	11.514%	$126.5126	$126.51	$126.50	$126.50
7 purchase totals =	$625.49		$675.9347	$675.93	$675.95	$676.00