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	$242.42	12.358%	$272.3783	$272.38	$272.40	$272.40
Purchase #2	$44.35	12.586%	$49.9319	$49.93	$49.95	$49.90
Purchase #3	$134.92	12.686%	$152.036	$152.04	$152.05	$152.00
Purchase #4	$51.80	5.467%	$54.6319	$54.63	$54.65	$54.60
Purchase #5	$49.34	10.112%	$54.3293	$54.33	$54.35	$54.30
Purchase #6	$146.37	6.225%	$155.4815	$155.48	$155.50	$155.50
Purchase #7	$173.95	6.247%	$184.8167	$184.82	$184.80	$184.80
7 purchase totals =	$843.15		$923.6056	$923.61	$923.70	$923.50