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	$247.89	13.833%	$282.1806	$282.18	$282.20	$282.20
Purchase #2	$82.84	9.260%	$90.511	$90.51	$90.50	$90.50
Purchase #3	$78.98	6.160%	$83.8452	$83.85	$83.85	$83.80
Purchase #4	$250.47	8.723%	$272.3185	$272.32	$272.30	$272.30
Purchase #5	$64.81	5.330%	$68.2644	$68.26	$68.25	$68.30
Purchase #6	$179.96	6.169%	$191.0617	$191.06	$191.05	$191.10
Purchase #7	$245.32	7.541%	$263.8196	$263.82	$263.80	$263.80
7 purchase totals =	$1,150.27		$1,252.0010	$1,252.00	$1,251.95	$1,252.00