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	$35.35	8.261%	$38.2703	$38.27	$38.25	$38.30
Purchase #2	$88.49	5.781%	$93.6056	$93.61	$93.60	$93.60
Purchase #3	$138.77	4.653%	$145.227	$145.23	$145.25	$145.20
Purchase #4	$77.49	6.758%	$82.7268	$82.73	$82.75	$82.70
Purchase #5	$69.45	4.549%	$72.6093	$72.61	$72.60	$72.60
Purchase #6	$109.44	9.243%	$119.5555	$119.56	$119.55	$119.60
Purchase #7	$243.25	10.572%	$268.9664	$268.97	$268.95	$269.00
7 purchase totals =	$762.24		$820.9609	$820.98	$820.95	$821.00