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	$82.64	10.455%	$91.28	$91.28	$91.30	$91.30
Purchase #2	$84.50	13.350%	$95.7808	$95.78	$95.80	$95.80
Purchase #3	$96.48	4.196%	$100.5283	$100.53	$100.55	$100.50
Purchase #4	$230.32	8.143%	$249.075	$249.08	$249.10	$249.10
Purchase #5	$133.90	6.235%	$142.2487	$142.25	$142.25	$142.20
Purchase #6	$144.34	5.736%	$152.6193	$152.62	$152.60	$152.60
Purchase #7	$71.74	9.535%	$78.5804	$78.58	$78.60	$78.60
7 purchase totals =	$843.92		$910.1125	$910.12	$910.20	$910.10