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	$97.32	12.464%	$109.45	$109.45	$109.45	$109.50
Purchase #2	$114.32	10.254%	$126.0424	$126.04	$126.05	$126.00
Purchase #3	$28.59	4.313%	$29.8231	$29.82	$29.80	$29.80
Purchase #4	$43.88	12.817%	$49.5041	$49.50	$49.50	$49.50
Purchase #5	$135.64	5.797%	$143.5031	$143.50	$143.50	$143.50
Purchase #6	$37.71	13.541%	$42.8163	$42.82	$42.80	$42.80
Purchase #7	$99.63	9.610%	$109.2044	$109.20	$109.20	$109.20
7 purchase totals =	$557.09		$610.3434	$610.33	$610.30	$610.30