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	$240.38	11.666%	$268.4227	$268.42	$268.40	$268.40
Purchase #2	$33.34	7.719%	$35.9135	$35.91	$35.90	$35.90
Purchase #3	$208.78	9.282%	$228.159	$228.16	$228.15	$228.20
Purchase #4	$111.99	11.197%	$124.5295	$124.53	$124.55	$124.50
Purchase #5	$117.96	5.647%	$124.6212	$124.62	$124.60	$124.60
Purchase #6	$60.55	12.181%	$67.9256	$67.93	$67.95	$67.90
Purchase #7	$154.86	9.786%	$170.0146	$170.01	$170.00	$170.00
7 purchase totals =	$927.86		$1,019.5861	$1,019.58	$1,019.55	$1,019.50