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	$10.45	8.322%	$11.3196	$11.32	$11.30	$11.30
Purchase #2	$123.26	11.433%	$137.3523	$137.35	$137.35	$137.40
Purchase #3	$203.78	7.434%	$218.929	$218.93	$218.95	$218.90
Purchase #4	$28.89	8.713%	$31.4072	$31.41	$31.40	$31.40
Purchase #5	$27.78	4.757%	$29.1015	$29.10	$29.10	$29.10
Purchase #6	$76.71	3.668%	$79.5237	$79.52	$79.50	$79.50
Purchase #7	$22.45	12.221%	$25.1936	$25.19	$25.20	$25.20
7 purchase totals =	$493.32		$532.8269	$532.82	$532.80	$532.80