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	$248.94	4.180%	$259.3457	$259.35	$259.35	$259.30
Purchase #2	$73.78	13.202%	$83.5204	$83.52	$83.50	$83.50
Purchase #3	$78.98	8.412%	$85.6238	$85.62	$85.60	$85.60
Purchase #4	$144.65	4.285%	$150.8483	$150.85	$150.85	$150.80
Purchase #5	$49.25	5.486%	$51.9519	$51.95	$51.95	$52.00
Purchase #6	$37.94	8.187%	$41.0461	$41.05	$41.05	$41.00
Purchase #7	$20.74	5.646%	$21.911	$21.91	$21.90	$21.90
7 purchase totals =	$654.28		$694.2472	$694.25	$694.20	$694.10