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	$98.37	6.698%	$104.9588	$104.96	$104.95	$105.00
Purchase #2	$213.54	5.107%	$224.4455	$224.45	$224.45	$224.40
Purchase #3	$242.42	7.736%	$261.1736	$261.17	$261.15	$261.20
Purchase #4	$107.69	3.171%	$111.1048	$111.10	$111.10	$111.10
Purchase #5	$217.81	5.572%	$229.9464	$229.95	$229.95	$229.90
Purchase #6	$38.42	9.550%	$42.0891	$42.09	$42.10	$42.10
Purchase #7	$60.85	9.597%	$66.6898	$66.69	$66.70	$66.70
7 purchase totals =	$979.10		$1,040.4080	$1,040.41	$1,040.40	$1,040.40