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	$27.55	5.149%	$28.9685	$28.97	$28.95	$29.00
Purchase #2	$58.96	3.573%	$61.0666	$61.07	$61.05	$61.10
Purchase #3	$101.92	9.422%	$111.5229	$111.52	$111.50	$111.50
Purchase #4	$27.30	7.507%	$29.3494	$29.35	$29.35	$29.30
Purchase #5	$209.59	3.189%	$216.2738	$216.27	$216.25	$216.30
Purchase #6	$180.39	10.293%	$198.9575	$198.96	$198.95	$199.00
Purchase #7	$56.94	13.392%	$64.5654	$64.57	$64.55	$64.60
7 purchase totals =	$662.65		$710.7041	$710.71	$710.60	$710.80