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	$240.25	5.840%	$254.2806	$254.28	$254.30	$254.30
Purchase #2	$157.47	7.271%	$168.9196	$168.92	$168.90	$168.90
Purchase #3	$38.56	8.863%	$41.9776	$41.98	$42.00	$42.00
Purchase #4	$18.92	11.779%	$21.1486	$21.15	$21.15	$21.10
Purchase #5	$36.58	7.809%	$39.4365	$39.44	$39.45	$39.40
Purchase #6	$80.56	11.205%	$89.5867	$89.59	$89.60	$89.60
Purchase #7	$227.57	7.492%	$244.6195	$244.62	$244.60	$244.60
7 purchase totals =	$799.91		$859.9691	$859.98	$860.00	$859.90