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	$12.69	3.693%	$13.1586	$13.16	$13.15	$13.20
Purchase #2	$135.98	12.234%	$152.6158	$152.62	$152.60	$152.60
Purchase #3	$9.51	12.392%	$10.6885	$10.69	$10.70	$10.70
Purchase #4	$201.58	13.540%	$228.8739	$228.87	$228.85	$228.90
Purchase #5	$212.90	13.727%	$242.1248	$242.12	$242.10	$242.10
Purchase #6	$80.66	12.413%	$90.6723	$90.67	$90.65	$90.70
Purchase #7	$133.78	6.794%	$142.869	$142.87	$142.85	$142.90
7 purchase totals =	$787.10		$881.0029	$881.00	$880.90	$881.10