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	$137.66	9.193%	$150.3151	$150.32	$150.30	$150.30
Purchase #2	$136.67	11.328%	$152.152	$152.15	$152.15	$152.20
Purchase #3	$133.39	7.824%	$143.8264	$143.83	$143.85	$143.80
Purchase #4	$70.89	12.156%	$79.5074	$79.51	$79.50	$79.50
Purchase #5	$169.87	5.807%	$179.7344	$179.73	$179.75	$179.70
Purchase #6	$90.34	7.641%	$97.2429	$97.24	$97.25	$97.20
Purchase #7	$108.28	9.720%	$118.8048	$118.80	$118.80	$118.80
7 purchase totals =	$847.10		$921.5830	$921.58	$921.60	$921.50