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	$60.34	11.243%	$67.124	$67.12	$67.10	$67.10
Purchase #2	$174.60	12.565%	$196.5385	$196.54	$196.55	$196.50
Purchase #3	$248.41	12.792%	$280.1866	$280.19	$280.20	$280.20
Purchase #4	$23.90	10.412%	$26.3885	$26.39	$26.40	$26.40
Purchase #5	$139.74	10.636%	$154.6027	$154.60	$154.60	$154.60
Purchase #6	$68.88	4.432%	$71.9328	$71.93	$71.95	$71.90
Purchase #7	$90.62	13.713%	$103.0467	$103.05	$103.05	$103.00
7 purchase totals =	$806.49		$899.8198	$899.82	$899.85	$899.70