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	$84.32	9.705%	$92.5033	$92.50	$92.50	$92.50
Purchase #2	$123.25	4.471%	$128.7605	$128.76	$128.75	$128.80
Purchase #3	$200.68	11.403%	$223.5635	$223.56	$223.55	$223.60
Purchase #4	$124.91	12.396%	$140.3938	$140.39	$140.40	$140.40
Purchase #5	$113.66	4.669%	$118.9668	$118.97	$118.95	$119.00
Purchase #6	$61.92	10.767%	$68.5869	$68.59	$68.60	$68.60
Purchase #7	$48.32	10.500%	$53.3936	$53.39	$53.40	$53.40
7 purchase totals =	$757.06		$826.1684	$826.16	$826.15	$826.30