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	$25.86	11.668%	$28.8773	$28.88	$28.90	$28.90
Purchase #2	$34.29	8.861%	$37.3284	$37.33	$37.35	$37.30
Purchase #3	$20.66	6.442%	$21.9909	$21.99	$22.00	$22.00
Purchase #4	$106.94	11.866%	$119.6295	$119.63	$119.65	$119.60
Purchase #5	$144.67	6.557%	$154.156	$154.16	$154.15	$154.20
Purchase #6	$27.56	3.156%	$28.4298	$28.43	$28.45	$28.40
Purchase #7	$229.96	11.145%	$255.589	$255.59	$255.60	$255.60
7 purchase totals =	$589.94		$646.0009	$646.01	$646.10	$646.00