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	$14.52	4.420%	$15.1618	$15.16	$15.15	$15.20
Purchase #2	$172.84	6.158%	$183.4835	$183.48	$183.50	$183.50
Purchase #3	$196.52	10.334%	$216.8284	$216.83	$216.85	$216.80
Purchase #4	$42.70	4.549%	$44.6424	$44.64	$44.65	$44.60
Purchase #5	$102.67	6.773%	$109.6238	$109.62	$109.60	$109.60
Purchase #6	$185.42	12.588%	$208.7607	$208.76	$208.75	$208.80
Purchase #7	$31.29	3.425%	$32.3617	$32.36	$32.35	$32.40
7 purchase totals =	$745.96		$810.8623	$810.85	$810.85	$810.90