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	$123.52	3.442%	$127.7716	$127.77	$127.75	$127.80
Purchase #2	$42.83	7.206%	$45.9163	$45.92	$45.90	$45.90
Purchase #3	$73.90	11.725%	$82.5648	$82.56	$82.55	$82.60
Purchase #4	$27.55	10.819%	$30.5306	$30.53	$30.55	$30.50
Purchase #5	$53.72	13.324%	$60.8777	$60.88	$60.90	$60.90
Purchase #6	$19.27	12.332%	$21.6464	$21.65	$21.65	$21.60
Purchase #7	$54.97	9.126%	$59.9866	$59.99	$60.00	$60.00
7 purchase totals =	$395.76		$429.2940	$429.30	$429.30	$429.30