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	$67.54	12.852%	$76.2202	$76.22	$76.20	$76.20
Purchase #2	$9.53	10.838%	$10.5629	$10.56	$10.55	$10.60
Purchase #3	$75.32	4.516%	$78.7215	$78.72	$78.70	$78.70
Purchase #4	$127.60	11.541%	$142.3263	$142.33	$142.35	$142.30
Purchase #5	$216.83	10.217%	$238.9835	$238.98	$239.00	$239.00
Purchase #6	$169.39	4.398%	$176.8398	$176.84	$176.85	$176.80
Purchase #7	$123.81	7.443%	$133.0252	$133.03	$133.05	$133.00
7 purchase totals =	$790.02		$856.6794	$856.68	$856.70	$856.60