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	$154.31	11.582%	$172.1822	$172.18	$172.20	$172.20
Purchase #2	$181.47	5.413%	$191.293	$191.29	$191.30	$191.30
Purchase #3	$234.47	3.196%	$241.9637	$241.96	$241.95	$242.00
Purchase #4	$70.70	10.772%	$78.3158	$78.32	$78.30	$78.30
Purchase #5	$141.80	4.147%	$147.6804	$147.68	$147.70	$147.70
Purchase #6	$41.72	9.115%	$45.5228	$45.52	$45.50	$45.50
Purchase #7	$31.54	5.430%	$33.2526	$33.25	$33.25	$33.30
7 purchase totals =	$856.01		$910.2105	$910.20	$910.20	$910.30