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	$108.28	8.402%	$117.3777	$117.38	$117.40	$117.40
Purchase #2	$14.55	9.449%	$15.9248	$15.92	$15.90	$15.90
Purchase #3	$250.40	10.790%	$277.4182	$277.42	$277.40	$277.40
Purchase #4	$55.27	7.466%	$59.3965	$59.40	$59.40	$59.40
Purchase #5	$107.99	4.489%	$112.8377	$112.84	$112.85	$112.80
Purchase #6	$37.89	4.260%	$39.5041	$39.50	$39.50	$39.50
Purchase #7	$171.92	9.552%	$188.3418	$188.34	$188.35	$188.30
7 purchase totals =	$746.30		$810.8008	$810.80	$810.80	$810.70