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	$108.39	13.660%	$123.1961	$123.20	$123.20	$123.20
Purchase #2	$57.74	8.792%	$62.8165	$62.82	$62.80	$62.80
Purchase #3	$125.41	12.253%	$140.7765	$140.78	$140.80	$140.80
Purchase #4	$33.31	6.187%	$35.3709	$35.37	$35.35	$35.40
Purchase #5	$66.78	7.251%	$71.6222	$71.62	$71.60	$71.60
Purchase #6	$133.50	3.565%	$138.2593	$138.26	$138.25	$138.30
Purchase #7	$27.53	7.555%	$29.6099	$29.61	$29.60	$29.60
7 purchase totals =	$552.66		$601.6514	$601.66	$601.60	$601.70