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	$236.53	11.775%	$264.3814	$264.38	$264.40	$264.40
Purchase #2	$155.44	9.192%	$169.728	$169.73	$169.75	$169.70
Purchase #3	$100.34	11.491%	$111.8701	$111.87	$111.85	$111.90
Purchase #4	$78.57	3.202%	$81.0858	$81.09	$81.10	$81.10
Purchase #5	$75.46	9.333%	$82.5027	$82.50	$82.50	$82.50
Purchase #6	$12.58	8.855%	$13.694	$13.69	$13.70	$13.70
Purchase #7	$53.79	11.771%	$60.1216	$60.12	$60.10	$60.10
7 purchase totals =	$712.71		$783.3836	$783.38	$783.40	$783.40