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	$29.45	8.402%	$31.9244	$31.92	$31.90	$31.90
Purchase #2	$227.75	5.497%	$240.2694	$240.27	$240.25	$240.30
Purchase #3	$81.57	13.767%	$92.7997	$92.80	$92.80	$92.80
Purchase #4	$49.58	13.601%	$56.3234	$56.32	$56.30	$56.30
Purchase #5	$111.68	10.546%	$123.4578	$123.46	$123.45	$123.50
Purchase #6	$153.99	8.496%	$167.073	$167.07	$167.05	$167.10
Purchase #7	$152.99	9.471%	$167.4797	$167.48	$167.50	$167.50
7 purchase totals =	$807.01		$879.3274	$879.32	$879.25	$879.40